This is a great idea. I think it could be incorporated into the Rifts, as they already send you to trippy places like Horazon's Dream and the like. You wouldn't have to actually travel back in time for this to work, although it could be implemented in a way that when you open a Rift you would have a chance to open a Time Vortex instead, or dare I say it, a Nephalem Vortex.