Bungie has a lot to be proud of, and I enjoy certain shooters (Halo, Borderlands) on controllers... the X360 controller is an awesome HOTAS unit.
But this REEKS of going mad with power. If the next consoles do not sell so well he is going to look very silly as they shoehorn mouse support in as a desperate last ditch effort to recover tens of millions in development costs.
Even restricting PC users to controllers for cross platform play wont work, as people will find a way to emulate it. that said, if it is co-op only who cares if someone has a better setup?
I really like the sound of the seemless instancing in destiny, look forward to some good co-op shooting.