It just so happens I was thinkin' about this recently. I was reading about how GURPS kinda fell off the charts during past decades, as SJG focused on Munchkin, and the OGL/D&D culture blossomed.
Here's what I would suggest:
1) That GURPS join the ORC Alliance, and release a GURPS SRD on the ORC license. So that new generations become aware of it.
2) The GURPS present itself as a complete one-stop system.
3) Toward that end: Convert literally every Open Game facet which is found on the 3.5 SRD, PF1 d20 archive (including the vast amount of posted 3PP open content), PF2 SRD and archive, and 5.1 SRD, into GURPS. From the start. In one gigantic book. Like major phone-book sized.
4) And also post official conversion documents /charts, and online conversion apps, for converting 5E characters into GURPS.
So that a person can feel that no matter how homebrewing their 5E or PF or OSR campaign is, they can see and trust that that one gigantic GURPS book has it covered. Bam!
For example, as a D&D Refugee DM, I'm running into some hurdles in converting our motley crew of PCs: banshee, half-ogre, frogperson, cowperson, wererat, leprechaun, awakened snake, awakened cat...not to mention all their classes, subclasses, backgrounds, inspirations, and all that. Which results in me wavering between various ORC systesms: A5E, PF2, etc.
This Open GURPS mega-book would have all of that.