I have been following this gaming industry for 32 years and I have been tracking Blizzard games since the last 16 years.
As a Blizzard follower since 2000: here is my prediction of the new MMO coming from Blizzard and based of what I saw in their latest technical advancements AND how Blizzard always builds upon earlier techniques in their previous games...
1. It will be announced at BlizzCon in 2013. Even in a playable form.
2. It will NOT be about science fiction nor a shooter MMO (too limited target audience, for example: women and elder people (40+) which are key players in present day MMO's and represent long term Blizzard fans).
3. It will use a server cluster instead of single server play, based on phasing and regrouping of players like we see now in region wide play in both WOW and Diablo 3.
4. It will have a region wide economy, no longer small server based. Not sure about RMAH, I guess that's a 50/50 option.
5. It will have NO predefined factions (but it will certainly have guilds), because it would hamper player integration.
6. It will have "levels" because D3 made it clear you need to include them to keep playing (paragon end game levels). It could be though that levels are no longer pure progression tools to advance to an "end game". Gear will still play a huge role in the overall progression.
7. It will have tablet integration in parts of its playing features. (like mini games but with advancing avatar tools).
8. It will be fully 3D like any normal MMO. Seamless open world will be standard. Probably no flying at the start, BUT full 3D rendered anyway unlike Vanilla WOW.
9. It will NOT include open sandbox tools, because Blizzard produces competitive games not tool boxes.
10. It will have PvP and PvE from the start and even the PvE will be competitive based (see Challenge modes) and supported by extensive profiles and Armory settings.
11. It will be targeted at HARDCORE players along with CASUAL players.
12. It will introduce a new quest/grind system based on advanced Monster Power strengths seen in D3 (patch 1.05). Set by players choices and probably based on personal phasing the solo play will be very challenging but can be tuned individually with harder/softer tuned mobs having more/less rewards.
13. The avatars will still be very role defined (tank/healer/dps) but with lots of solo options in adaptable challenge modes (see point 12).
14. It will have its own history but set in more modern times then WOW. Likely Period: late 19th Century with alternate history lines.
15. It will have a multi subscription based system along with other Blizzard games (combo subs).
16. It will gather the most deepened hate campaign at Metacritic months/weeks before launch.
17. Wow players will be offered limited Beta access during the last year of Beta (starting in mid - late 2014 and announced in the last months of MoP).
18. It will gather with ease more players in its first year than WOW.
19. It will launch globally one year later then predicted, probably around mid - late 2016.
20. It will generate a new massive interest in MMO play just like WOW did back in 2004. But this time with integrated tablet support and region wide play.