I think the complexity involved would be too much. I may be wrong, but there seem to very few in number developers working on UO now. Personally, I'd rather they work on producing high resolution and updated imagery for the CC. Personal preference, of course.
Because that would cost millions and millions of dollars and wouldn't make sense even if you were willing to spend the money. The games have virtually nothing in common other than being RPGs where people fight things. Writing a new 3D engine from scratch would be easier than trying to bolt non-instanced houses, ships, etc. onto the SWTOR engine.
These devs can't get anything right and you expect them to make yet another new client?? Yikes.
Waste of time and would be worse for the game, as evidenced by previous failures. The 2D artwork is timeless and ages better than anything 3D.