Established 25m guilds can continue as always, but in the end, shared lockouts was THE catalyst for the "death" of 25mans, that's all. Back when they gave better items, cooler titles and mounts, and the option to also run 10s for additional gear was more than enough to entice guilds to build a 25m team, nowadays the logistic ease of 10ms and lack of enticing rewards makes 10m much more appealing to most guilds.
Personally I don't really care, I think smaller raid groups are more interesting, two tanks, two-three healers, 5-6 dps, and every single member matters, whereas 25ms are generally the same, slap on a few extra healers and a whole bunch of zerg-dps
EDIT: A bit surprised no one has noticed this yet, considering how many are apparently commiting seppuku because of getting last years anniversary letter (bug)
The 8% is useless, yes. 8th anniversary.
Last year it was 7%. It's just a number-thing, not a significant bonus