Starfinder was fun in a 3.5 way, but I found the leveling weapons way too strange and restrictive. I liked it better than Pathfinder 2 because the game was way more familiar to me coming from Pathfinder 1e, and it does not stray too far from that core experience. If I had a good character creator program on a desktop system (Hero Lab 2), I would probably still be playing this. Another benefit is most all the old Pathfinder 1e books are still useful, with this being a legacy 3.5-like system.
Would I convert this to GURPS?
No. You can't convert something this big would be the answer, and realistically all you could do is use the races, monsters, and pawns for GURPS: Space. Keep the look and races, return the elves and dwarves back in the game thank you very much, and make everything like a Heavy Metal movie and we are all set. So, no, I wouldn't. But I will use the Heavy Metal idea.
Starfinder's world always left me wanting more, which is why I played a Star Frontiers-Starfinder mix. I like a set universe and a melting pot of people living in close quarters and that have to get along. The Guardian of the Galaxy style "hyperspace to anywhere" random planet of the week feeling never really appealed to me.
I would rather play in my own universe of a series of destroyed worlds, all with factions eternally at war with each other, and the players have to pick sides and survive. The Starfinder society and all these structured governments and social order never really felt right to me either, to me, Starfinder is at its best in a chaotic, messy, kill-or-be-killed science-feudal world that is more like Heavy Metal: The Hexcrawl and less like Guardians of the Galaxy-Like: The RPG.
People living out of the wreckage of massive crashed starships, with villages built around them. A diverse mix of every race in the universe, kind of the like Star Wars cantina scene but just everywhere. Constant wars and battles everywhere. Ruins of lost civilizations, some 1-year-old others 1-million years old, are scattered around on these random hex-crawl worlds. Starships that are 15,000 years old are sitting abandoned in ancient temples. Monsters eating people everywhere. Techno fortress walls. Insane robots (overused, I know) wandering the wastelands killing things on sight.
The current structure of the Golarion star system, the great memory wipe, and all that structure and government just feel too restrictive and metaplot to me. Like there are "star cops" out there enforcing arbitrary laws, and huge space governments telling what you can and can't do.
Our old Star Frontiers game devolved into space politics and "can and can't do's" and I have this allergic reaction to game designers building structured sci-fi settings with rules, borders, and massive space fleets.
I get this feeling my problem with the game was rooted in the adventure paths and their constant use of governments, missions, space laws, and structure. If this was like any Pathfinder homebrew world and I could toss all that "Starfinder structured society cruft" out I would have liked this a lot more. Space Elves. A Drow empire that lives in asteroid caves. Dwarves that live in the molten cores of worlds.
Cool stuff. You have magic and fantasy races. USE THEM.
And billions of space citizens without homeworlds, governments, or places to call their own. Endless wars where you barely know who is who and what the heck they are fighting for this time. Take some of the monster pawns, even from Pathfinder 1e, and make them character races as well. Kingdoms of the lost trying to build their home out of the ruins of worlds that have never seen peace in a million years. In a world like this, characters can be kingmakers and heroes instead of pencil pushers and FedEx drivers.
And don't limit the weapons arbitrarily. This is like Heavy Metal, a level 1 space goblin can have a level 17 blaster and blow away the PCs with one pull of the trigger. That weapon is worth a lot of money, sure, so it is both useful and treasure to buy upgrades for everyone. If you can find a reputable buyer.
And add a killer rock soundtrack.