CN server has a campaign of asking the devs, too. The most recent two rounds are about Mists and some answers may be of certain value. So here are what I translated from the official threads of official Chinese WoW forum.
Sources（all in Chinese）:
Q: In the current beta of Mists, only female pandaren get to choose lesser-panda model (with the tail) while male pandaren cannot choose the tail. Are there plans to add it to the male?
A: Male pandaren may choose lesser-panda model, but without a tail. We want to make tails unique for female pandaren.
Q: Are there other objectives besides time attack in challenge mode?
A: We are not adding challenging objectives like the achievements of heroic dungeons for now. However, the damage and HP of monsters in challenge mode are significantly higher than heroic mode. The clock is not so ticking if just for bronze medals, so the bronze challenges are more about the difficulty of dungeons and the use of CC abilities. Silver and gold challenges are more about racing against time.
Q: Will we be able to steal people's crops in the WoWVille game of the Tillers?
A: No, you are the only one who can see your farm.
Q: Will there be more faction-themed mounts (e.g. Armored Razzashi Raptor and Rivendare's Deathcharger)? Some complain that Alliance can have more Horde-themed mounts.
A: The design we apply now is to make sure both factions have all the new mounts. After all, even in the old days, all that it took to collect all the mounts was but a lot of time investment.
Q: Are monk trainers in non-pandaren starting areas pandaren too? Can we expect to see pandaren in the places other than Wandering Isle and Pandaria, like in the quests of leveling from 1 to 85?
A: According to our current plan, all the monk trainers will be pandaren. But players are not supposed to see pandaren NPCs except starting areas during the time they level from 1 to 85.
Q: Are there plans to adjust the speed of XP acquiring? Or lower the XP required to level from 60 to 80?
A: It's hard to say. The current leveling speed is already too fast. Many players switch to next area so quickly that they cannot have full quest lore. But we might adjust the quest routes of LV 60 to 80 so players can choose the route they want.
Classes and systems
Q: In Mists, Druids have many new shapeshifting inscriptions. Why do Druids get more fun stuff than the other classes?
A: It's easy to give Druids more choices of appearances, all we need is to invoke another model when they shapeshift. But it's not that easy to put this on other classes. However, we still managed to give other classes some eye-catching minor inscriptions. We also hope to introduce a class quest so warlocks can unleash green felfire.
Q: I heard there would be archaeology dailies. Are these dailies available only when archaeology skill reaches 525? Or is it like the fishing and cooking dailies in Cata, which merely require minimum skill points?
A: The latter. Archaeology dailies are like fishing and cooking, chosen randomly from 3-5 quests every day.
Q: Is there a reputation requirement to use elder tokens to buy gears?
A: No. You will be able to use elder tokens to buy gears from specific NPCs. These elder-token gears are different from the rep gears sold by rep vendors. Besides some gears that require certain levels, you can buy many enchants from these NPCs (which are provided by rep vendors in Cata). Rep vendors will also sell some rep gears like before (cost gold, not elder tokens), and these gears require certain level of reputation.
Q: Will thieves and warriors still be able to acquire and equip ranged weapons (not from LFR, because ranged weapons are supposed to be more “suitable” for hunters)? Many warriors worry that after the launch of Mists they can no longer run Sunwell to farm Golden Bow of Quel'Thalas.
A: Thieves and warriors will still be able to acquire and equip ranged weapons. It's just that they cannot acquire ranged weapons from LFR.
Q: What will happen to the currently existent resistance gears? Will resistance become something else on the gears?
A: We will remove resistance from most resistance gears. But there may be some gears that still have magic resistance. For now we are not so worried about it since these gears are way too old.
Q: How about the world-drop enchanting recipes and the resistance enchants for weapons and the patterns of resistance gears?
A: Do ditto. There might be some enchants and patterns that are left behind, but they are not our concern.
Q: Is it possible to introduce the option of invalidating Alt+Tab combination like SC2 does so players who do arenas or raids won't accidentally switch to desktop? Such accidents are quite usual because many players would put Alt in their customized hotkeys.
A: Currently we don't have such plan. Our UI setting is already too complicated.
Q: Will there be some upgrades of graphic engine in Mists?
A: We further enhanced rendering, shadow and environment fog. But they are not so distinct. We may consider giving a detailed list of changes or some before-after comparison screenshots.
Q: Some players feel empty during the time of leveling from 1 to 85 because of the acquiring frequency of skills and talents decreased. What do you think?
A: The frequency to acquire skill is as high as before, if not actually higher. After all, those skills that used to require talent points are available from your specialization directly. A most different part now is players do not click talent trees once every 1 or 2 levels. But we never considered it interesting to have players to choose to add 1% damage to their frost spells. We plan to introduce a concise window to tell players when they can learn a certain spell. However, the new talent system is indeed more important to level 90 characters than the leveling characters.
We will introduce the similar mechanics to dungeon unlocks.(e.g. a LV15 Horde character will receive a message to tell him/her that Ragefire is accessible now)
Q: Will the volume of void storage increase?
A: Currently we don't have such plan.
Dungeons and raids
Q: Is there going to be a queuing system for challenge mode dungeons like the normal and heroic dungeons?
A: NO. Challenge mode will be extremely difficult, you have to challenge with a team that you are familiar with. Our current design philosophy is that once a member goes AFK after entering the dungeon, you guys will have to start over.
Q: Is there going to be some conditions to enter challenge mode? Since all the ilevels of gears are normalized to a fixed extent, will there still be something like an ilevel requirement?
A: By then there will be a minimum ilevel requirement, maybe higher than heroic dungeon.
Q: Will the loots of new Scarlet Monastery include Tabard of the Scarlet Crusade?
A: We are considering that. We want to reserve some distinguished old items.
Q: Idealistically, how long will it take for a PuG to complete a run of a heroic dungeon in Mists? You mentioned earlier than the difficulty of heroic dungeon would be close to the ones of WotLK, so how about the time taken?
A: The time needed to complete a WotLK heroic dungeon varied greatly from the time this expansion launched to the introduction of LFD. In Mists we believe 30 to 45 minutes is an ideal average value.
Q: Could we have nunchucks in game please?
A: Currently there is no such plan. The physics of this weapon is way too complicated.
Contents and Functions
Q: Will there be any rules about pet trading? Will we be able to trade pets of limited editions (like Panda Cub) or Blizz Store pets（like Wind Rider Cub）? How about achievement pets?
A: We plan to allow players to trade Blizz Store pets excluding Guardian Cub (because it's not BoP and it's unique). Collector's edition and other limited edition pets (like Mini Tyrael or BlizzCon pets) will not be tradable, either.
Q: Will we be able to rename a pet after we name it?
A: Yes, that's the current plan.
Q: You said earlier that not all pets can take part in pet battle system. How about now? And what are the exceptions?
A: Currently the exceptions are pets with humanoid children models. They will not be included in pet battle system. Nor will Guardian Cub.
Q: Scenarios seem fun enough. Will they provide some solid rewards besides VP and rep? And are all scenarios accessible only to lv 90 players?
A: Given the simplicity and convenience of Scenarios, VP and rep are rewards that are solid enough. Current scenarios are accessible to lv 90 players only, but we might introduce some low-level scenarios in future.
Q: Compared with WotLK and TBC, leveling from 80 to 85 in Cata is significantly faster. How about MoP?
A: It's hard to predict before the game goes live. In average we think it won't be faster than Cata since you are not allowed to use flying mounts during leveling. So the time taken should be a little bit longer.
Classes and Systems
Q: Some players think it's not a good idea to have Mistweavers healing while damage-dealing. Have you considered other devices of gaining chi?
A: We won't force Mistweavers to do so. It's only an optional game style, just like Atonement Priests healing with Smite. In some special encounters, Mistweavers can totally stay in the back of the raid with other healers. We haven't completed all the skills of Monks so chances are some other devices of gaining chi can be added in.
Dungeons and Raids
Q: The number of 25-man raiding guilds seems declining (In some players’ impression). Are there going to be any plans to encourage them? Or do you plan to remove 25-man raids?
A: The number of 25-man raiding guilds is probably going to keep decreasing., but we will still continue to provide 25-man raids unless one day no one does 25-man raids anymore. We do not have direct plans to encourage players to choose 25-man. We hope to keep 10-man and 25-man raids close enough so players can choose the type that they find interesting. (Provided you have enough people to run 10-man or 25-man raids)