This is going to destroy 25-man raiding, but not because of gear.
Every serious 25-man raider in my guild enjoys running 10-mans for fun, or to blow off steam from 25-mans. With their removal from the game, no one is going to want to be part of a 25-man guild. The 10-mans will simply be more relaxing, and have similar rewards.
My guild has been together for over four years. We raided MC, BWL, and ZG together. This could very well be the end.