It's a interesting idea to place Vader/Luke/Palps on Coruscant for the final battle and would make for a much more interesting backdrop......but I can't see it working.
I know changes to the core story are in order but this one change I can't see fitting. Too many other things would need to be reworked or edited out for it to function. Plus - as it has been mentioned - the Emperor being on the DS2 is the rebels main reason for giving it their all.
Without the Emperor on the DS2 all we have is a rehash of AnH (rebels blowing up another space station) which is something we are trying to get away from.
Even with that said I'd still like to see a mock up of what it might look like.