Speaking as a fan of the WOTLK/Scourge story, I've been hoping that we'd see a return to the continent at some point because the ending of Wrath didn't feel like definitive closure. It still feels at least to me that there is a story left to tell. I don't think it has enough legs to do a complete expansion from it but maybe like part of an expansion or a content patch.
Three main things at play here which lead to believe it could work well.
- Cataclysm did a lot of damage to EK/Kalimdor, why not Northrend? There is an entire spider kingdom underneath Northrend so who knows what else is buried under that ice.
- Bolvar's already pretty unstable now, but surely dominion over the scourge has to run out at some point?
- All the killing that happens in the world every day, it's just asking for someone to start making new scourge!
The story perhaps would be the Cataclysm has over time caused the thick ice below a part of Icecrown to crack and has uncovered a previously dormant breed of scourge that the Lich King had previously imprisoned as he couldn't fully control them. Their reemergence would lead to a sort of civil war between Bolvar's scourge and this new scourge army in a phased version of Icecrown. The point would be trying to find a 'cure' to kill off all the scourge once and for all. The idea that the Alliance and Horde would leave a threat like that still standing is funny so it would in my opinion be a great way to tie that loose end once and for all.