out of those ive proposed 1, 2, 4, and 6.
i think they would all be awesome,
i dont think we will see any crossovers in the franchise that is cannon, and wrathion is an antihero so i doubt hes evil and it would really suck if the guy weve become friends with an entire expansion would be turned into a bad guy.
right now though i think we only have two real options for the moment
burning legion
or
south seas.
while something like the void who eat planets, or the titans, or old gods in space would be awesome and are pretty much inevitable i think before we go off to another world we need more content hinting at the fact a good portion of azeroth CAN go off world (yes i know draenei have the exodar working and tempest keep, and yes i know the ethereal but you dont really see humans and dwarves and orcs flying spaceships do you?)
i think a burning legion expansion where we are exposed to these things more and the races of azeroth become more accustomed to them would help set off one of those expansions without a "lolwut i can has spaceship?" moment happening.
---------- Post added 2013-05-17 at 03:42 PM ----------
except pandaren were in the original warcraft lore.
chen stormstout along with rexxar helped build orgrimmar and if it wasnt for them fighting on the frontlines against daelin its likely the human forces wouldve overtaken the orcs.
not to mention the reason night elves have a heavily asian inspired culture instead of the mayan culture of their ancestors is due to the former alliance and trade between the pandaren empire before the pandaren shunned them and closed their borders.
also pandaren were integral in the creation of brewfest.
all of that happened in lore pre mists information by the way either in rpg books or in warcraft 3. and before you say "RPG NAT CANNAN BRAH" those three things i listed are now cannon so it doesnt matter that they originally came from the rpg books they are ingame now.
not to mention bubble bobble isnt even an anime or manga, its an old school video game