Actually, my group transitioned a D20 Modern campaign over to Saga and it worked pretty damn well. As well as a Zombie-Apocalypse themed campaign, very funny an easier to play along with that d20modern. Saga simplicity is very very helpful to bring new people into RPGs as well.
There's some differences but overall, just make sure you get a few of the Alternative Class Books so the non-Jedi classes have enough Talents to keep the game interesting. Also, The Force is an implementation of an effective SUPERNATURAL/MAGIC game mechanic. Arcane check, Divine check or even Psychic checks are handy ways to convert your favorite abilities from whatever fictional material you prefer. If using the force somehow still crosses your mind.
In SAGA weapons loosely break down like this, compared to d20 modern :
Simple Weapons deal 1d- of Damage
Advanced Melee Weapons and Inferior Ranged Weapons deal 2d- of Damage
Normal Ranged Weapons (Blasters in Star Wars) deal 3d- Damage.
In d20 Modern and Equivalents most "Normal" Ranged weapons deal 2d- Damage but since in SAGA most characters have more HP than they would in d20 Modern the 3d- balances better.
Oh and as far as Classes go just use them straight out of the book... except for Jedi the "Noble, Scoundrel, Scout, Soldier" breakdown of SAGA works perfectly for most settings.
Cybernetics can be ported over from d20 Future, along with mutations. SW never did enough for gadget-minded PCs, and I think this helps. Also, they're slots to fill with rewards as the campaign progresses. It has great limitations on what to use according to your level.
I found some people who ventured into similar use of SAGA, converting the futuristic "Mass Effect" video game to saga rules, It was converted by some guys at he Giant in the playground forum :
http://www.giantitp.com/forums/showthread.php?t=282956As for Saga Edition going into a universal GURPS style game system, or some sci-fi Shadowrun oriented game -- maybe you can see Gary Sarli's E20 Evolved. Very complex to my liking, but you may find something useful.
Importantly, please keep us informed on how you develop this concept and how it plays out. Im personally interested to help other players enjoy SAGA if some conversion guidelines could be shared.