So we all noticed I hope, that we can roll a Force Die in a lot of talents and forces, adding skill (opposed and constructed). How would you accept a home-brew universal use?

Basic for me would be an alternate Enhance force power (Like Foresee and Warde's Foresight in CotG), but I also have cheesy ideas about a talent trees with a lot more varied talents of this type

A coin for your thoughts!

It shouldn't apply to Combat skills (Brawl seems to be the exception), especially Lightsaber.

Yeah, there's a very good reason why you can't add Force dice to combat skills in general. Brawl gets a pass because generally speaking, Brawl is a very sub-optimal approach to combat as unarmed attacks do far less damage than even most Melee weapons, and frequently come up short against Ranged (Heavy) weapons or even your bog-standard blaster pistol. And you've got lightsabers, which when fully modded are some of the most devastating weapons in the game (only auto-fire weapons and distruptors give them a solid run for the money in my opinion).

Plus, with FaD it's possible to have characters with Force Ratings well above a 3, which was the effective cap at the time Enhance was first published in Age of Rebellion. If anything, adding a Control Upgrade to Enhance to let you boost up Brawl checks was a way to make Brawl a not-so-shoddy combat option for Force user PCs. So being able to roll 5 Force dice on a Lightsaber combat check veers much too close to the "first hit wins!" scenario that plagued WEG's D6 system in regards to lightsaber fights between experienced Jedi, where someone like Vader could easily destroy a starfighter with one swing of his lightsaber based upon how damage worked in that system.

Plus, there's already a Force power that lets you boost combat checks in general. That'd be the Sense power with it's final Control Upgrade to commit a Force die and upgrade your combat checks. And since you'd need to purchase the Strength Upgrade along the way, you'd get to upgrade the check twice for the cost of one committed Force die, leaving your other Force dice free for other things and providing a slightly more consistent result; if you've got more than one rank in the skill and a characteristic higher than a 1, then you're effectively adding a proficiency die to each check with that upgrade active.