Wouldn't be so sure about Bard's being put to work...I'm betting one of the new classes has a target-able mp refresh version of goad.
This is the most likely happening. People talk a big game but I can't imagine that DRK is going to bring a boatload of new people to tanking on any more than a temporary basis. Certainly people will flock to the new stuff, but there'll be three new shinies all at the same time.
I'm sure, at Heavensward, lots of statics will shake up roles and the like, but I just don't see the tank population changing much in proportion to how it is now.