One thing I've noticed on my realm are the number of guilds that are moving from 10-man to 25.
Raiding is inarguably more accessible now a big swing from BC attunements that required 5-man milestones that many groups couldn't (or didn't bother to) reach.
Now the type of player who claim they only want to do instances with their 10 friends, are starting to branch out and up.
Guild #29,358 downing the 4 Horseman isn't going to make its rounds on wow blogs and websites but I don't hear wow losing any numbers.
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