If i were you i woudn't expect huge change, since Cataclysm are just another expansion, but have some good beta video from youtube, will post it in another topic soon.
And there's people quit WoW every week due to several reason, some cannot afford to paid anymore, and some people might get bored or after all they just want to play good MMO but they're prefer free stuff so LOTRO and many of free MMO are their solution.
Number of player are uncertain, it's up and down for everyweek, and if other MMO gaming developer company push hard in marketing, at least they can lure many people to play their games instead of WoW.
And by this new, it isn't mean fully 100% to play, Blizzard use some itemmalls system and might finally force people to paid again though cheaper.
Still i woudn't agree less about "million years..." or "over two billion" Blizzard can dig alot of money from WoW...and they won't destroy their gold mine.
One thing that's certain, it'll be free...probably someday in the(not near) future, when other gaming developer company push hard and making MMO that can match WoW, though Blizzard may make it free...they might put some trick into it and force people to paid again.