I wouldn't mind it, I like flipping the roles and there's no reason why you can't win these fights, since heroes are just NPC's like raids already are.
I think it would be hard to implement into WoW though except for scenarios like Illidans memories... but those are bit more scenic rather than gameplay rich.
So I like these ideas, I just don't see how it can fit into WoW. Why would our character suddenly become a raid target? If we make new characters for this, why would we suddenly play like them, etc etc...
I think in the end it would play like the mage tower challenges actually now that I think of it.