Don't worry, when we switched to WotLK back in '08 the Lich King, as well as all major threats, were dead. Thus killing just about 98% of the chance for RP in Northrend outside of Dalaran. Cata is being done so that we are only a few months after the Cataclysm began, thus every major issue is out there waiting for the brave guilds and individuals out there to slay them.
For instance, there is a lot of fighting going on at
Tol Barad. Before too long, it will become an active PvP Zone with full events revolving around that. For now, it's mostly PvE events, until the Horde and Alliance meet and clash.
I believe there is a guild taking on the problems of the Twilight Highlands right now (I can't remember, I want to say Lion Hearted or the Regiment, someone from this can tell you more.) That one is Alliance and @Brutalskars is working on getting a Horde equivalent up and running in Twilight Highlands with his Bloodsworn Honorguard.
I think @Nikodemos has or had plans regarding Uldum, not sure on that though.
I haven't heard anything regarding Vashj'ir, but there is always the possibility of using that zone for awesome events and Rp!
I am sure that there is some Night Elf guild gearing up for Mount Hyjal, or at least I hope there is!
And Deepholm? I am not very sure. Kind of a strange region to really do anything if you aren't a Shaman/Druid/Mage or something like that. But who knows?
Not to mention how about 65% of the world (excluding Northrend) has been changed either by War or by the Cataclysm! So the possibilities are endless for all manner of things, at least until we get geared for Mists in the distant future. At some point I am sure they'll say "Oh yeah, some elite peeps and their doo-dads killed that big ol' Darthwang. The world is saved!... for now."