I don't care what drive set-up it is. I mean, RWD would be cool, but Devilles have been FWD for how long now? It should be expected.
As for size, as long its as big as the Deville I have now it will be fine. 211 inches is a good size.
But the deal-breaker for me will be whether or not it has a V8. Standard or option, it has to have some way that I can get a V8 in it from the factory. If not, then the Audi A8 will remain my #1 choice for full size luxury.