I'd rather they reprint 3rd edition than make a new one. I hated 4e Gurps in just about every way. Way, way more complicated than I wanted and the artwork was an abortion.
I am firmly in this camp myself, but every time I bring it up someone will educate me about how much better 4th is...
4th is so much better.
Oh well now that that's out of the way, my ideal GURPS isn't set up like 4e but I do like the idea of a really complete rulebook, as long as Vehicles is Core Set volume 3. Mechanically I'm mostly happy with fourth, Personally, I'd change ranged combat, I find people really hate it an I'd list skills as stat - 2 etc rather than "easy, average, hard" then the chart would be just two columns and if anyone finds that impenetrable, I swear I'll punch them in the face.
If you want a one book point of entry, something like 3rd edition is the way to go. I think you need to cover fantasy in the core, at least enough to get people to try it. That's the one weakness I see in GURPS lite 4e is that you can't play a basic fantasy game with it.
Ideally, Lite would be the core. Bulk up the page count a bit with art and a little more discussion on how to use all this stuff. But every book should be usable with nothing more than lite.
The biggest problem fourth edition faces is that it's far too much for new players to get into. I don't mind the idea of an ultimate reference work but ideally it would be a database where you could select elements to generate and print out a book to give your players.