The most basic stuff would to be overhaul the saber system so it's not just a console hack 'n' slash button mash fest, and to give it a robust multiplayer component (using the original Wii version as a base for ideas but not the final word... obviously FU2 is out, as its multiplayer was basically Smash Bros. with Star Wars graphics).
Little things on the PC version would be nice like scalable graphics options, use the mouse in the menus (most pc gamers don't exclusively use an Xbox360 controller, that's another thing that's got to change, support for many more controllers than the ones they included), and a crouch option.
Make it 60 fps and improve the controls. Let us actually fight the cool bosses, don't rely so much on QTE sequences. Improving the saber system and controls would make this part work better (I presume they put them in because the fight system was so limited and tedious to begin with).
Otherwise I'm not sure what else to add. As long as the story, characters, and so forth are good, it'll be a worthy installment in the series if it ever gets made.
Right now TFU series on the pc seems like a poor man's JA with next gen graphics and gimmicky physics. The gimmicky physics are fun, but the rest of the game could use some work.
I think they had the right idea with alternate scenarios in the Ultimate Sith Edition. The point of these Star Wars games is, whatever the story happens to be, we really want the option to screw around in the situations and areas of the movies (not ONLY that of course, but that's a main draw for Star Wars fans, always has been, always will be). So you can have an original story, characters and so forth, but you have to let us do star warsy things along the way (not saying blatantly copy the movies, but look at the stuff on the USE with the DLC, that was great stuff).