I think it's fair to say that most of the better guilds have started preparing for the upcoming mythic raid difficulty. 10 man guilds are most likely to bolster their ranks with new recruits, or merge with existing 10 man teams. While a lot of 25 mans will simply cut down on their current roster with a few replacements here and there.
Who do you expect to take over in the race for world first? What are your expectations for the general raiding population? What will be the deciding factors when it comes to who feels more "at home" in the 20 man setting?