It's already been confirmed that both Shadowfang Keep and Deadmines will be made heroic, mostly for their own story purposes. This poses an interesting thought -- what other instances could be made heroic, and why? Since we know that Desolace is going to be green and lush, maybe they'll do something with Maraudon? (I'm not sure who would want to see Princess Theradras again, but hey.) Perhaps a heroic Blackfathom Deeps, considering that the Twlilight's Hammer is making such a big comeback in the next expansion? Or hey, why not even a heroic Razorfen Downs? Why? Why not, I say!
So, dear readers - what old world instances should be given the heroic upgrade, and why? Personally, I think I'd rather stick hot pokers in my eyes than see a heroic Wailing Caverns, but that's just me.