If they do end up making a new JK game I would like to see some more open game play (maybe in the line of massive maps like those in GTA style games or even KOTOR, where you can choose when you handle major story based missions and whether you want to handle smaller missions, like bounty hunter missions or small quests), but I would like it if they would keep the current style of combat. After all these are not RPG games they are of a more action based genre. I would also like to see a more advanced system for vehicles, something along the lines of what they have for Battlefront 2. If they make the games more open like this, then it would also provide for a longer, more involved SP game experience.
The only other thing I would like to see is a more advance character customization system, with more species and the ability to alter facial features, clothing, tattoos, and physical attributes like strength and weight. Also, it would be nice if you could actually build and customize your own saber, rather than just choosing from already constructed designs from the game designers.
Of course, if they were to actually make a game like this it would be massive. Most likely involving three to four discs for installation at least. But I am sure that such a gaming experience would be great.