Having finally gotten Empire Total War working on my computer, and playing it for the last few hours, I have come to an interesting conclusion: The Total War engine, with slight modification, would be a wonderful platform for a Star Wars version of the game. Now, I'm sure you're thinking to yourself: VG, we already have that in Empire at War. In one sense, yes, you are correct. EaW is the latest iteration of the full empire-building game, complete with space and ground combat, but there's frankly little strategy in that kind of combat. Total Was is about far more than micromanaging units, it is about the entire feel of running an empire and commanding troops.
If Empire Total War has shown anything it is that a non-ground based combat style is possible (via the naval warfare). This can be translated into space combat with some modification (handling of the 3rd dimension in space has always been tricky, even in EaW. This would make space combat largely doable in the Total War engine. Since damage tracking is also done and directly effects mobility and firepower, this too is doable for starships. Ship capture, which simply hasn't been done effectively in a star wars empire game, is also very possible (let's face it, the rebels relied heavily on captured star destroyers).
Ground combat could be a little trickier, though. Total War has not used any sort of aerial combat to my knowledge, so straffing runs and aerial reinforcing from the fleet would have to be added. I think it is vital that any reinforcing not be done automatically (as is the case with Empire Total War). There should be an option to call in reinforcements, or hold off on doing so. Another major addition will be vehicles. Canon are good analogues for many of the turrets and defense systems that would be used, but thinks like the AT-AT and AT-ST are a little more difficult to introduce, as no unit currently mimicks them in any way. Since they are motorized vehicles, damage to them would function more like ships than anything else. These could also be capturable (a la Chewie on Endor).
Jedi pose another problem. The Force is also something that is not in current Total War games, but there are ways to think about force powers. Lightning or single-target killing powers are the mechanical equivalent of a gunshot, and force throws and knockbacks are similar to artillery fire. Give hero units more effective armor and/or more health and you have an effective hero unit that functions like heroes in any other star wars empire builder.
As per planets, you can treat them exactly like provinces are treated in every Total War game. Have them function as a city surrounded by a zone, except in this case the city is a planet and the zone is an area of space.
In all I think that Star Wars: Total War is completely doable. I do not, however, think it will ever be done. Games like EaW satisfy most audiences and Total War is a far more reality based game series. Not to mention the fact that any new Star Wars games will detract from Bioware's MMORPG, and Lucas Arts has always been careful about releasing games for maximum coverage and profit. Do I hope that it happens? Very much so...but it simply will not.