the main reason the went to 25 mains is because they wanted more of their player base to experience the full extent of the game, as its easier to get 25 people together rather then 40. Theoretically. however its totally backfired IMO, for those guilds that could do AQ and naxx pre BC, it became a logistic nightmare having to downsize, luckily our guild didn?t have this issue as when TBC came out a number of people either stopped playing or xfered to be with fam/friends,
Kara IMO is too long for a 10 man, and pugging it is not really going to happen, on bloodhoof i don?t think ive ever seen a LFG kara, if you aren?t in a guild you aren?t running it, its also not that easy, i don?t foresee "casuals" clearing the instance, fights like curator, prince and netherspite take a bit of coordination and teamwork, being a 10 man is fine, we used to run 3 groups in it like many guilds, I just think its too long and there is too much trash, especially between curator and shade
Originally the first 25 man encounter (Gruul) was nearly impossible, so they nerfed him a lot, and now hes cake, the 2nd Magtheridon is still a major PITA and in its current state will be impossible for anyone other then a pretty decent raiding guild,
SSC is a whole nother game, as someone on the WOW forums said, blizzard made all this new content that no one other then the top guilds will ever see, Hydross still stops many serious guilds and is something casuals will never see downed unless its changed dramatically
Heroic 5 mans were a good idea that was implemented badly, as some of them are still harder then they need be, and are too luck based, as trash mobs shouldn?t hit harder then a 25 man raid boss, apparently this is being fixed in the next patch
And PVP got better with the arena, it gave those that just wanted to PVP something legit to do that gave PVP based rewards, world PVP still happens, people raid towns now that DHKs are gone