The flying Ford Anglia would suit a Robocoaster reasonably well, but there were talks of a Hogwarts Express theme ride, which to me, says rollercoaster and not robocoaster.
Incidentally, I think the robocoaster rumours have only surfaced because of Universal owning the rights. I think that the Robocoaster would be much better suited to USF. Also, considering the old BTTF, a clever cannibalisation of that building would allow for a good few robocoasters to built in that building without the need for a whole new building. Simpson's Robocoaster, it might work.
As for a DD retheme, if they did that, then what exactly would LC have left, I can't see a DD re-theme happening unless LC is lost. However, there is some space around the back of DD which they might try and use somehow, this would mean themeing a few of the sheds and stuff that DD uses.