As one might imagine, many GURPS fans have lots of opinions on this question, and there has been a lot of discussion on the topic. Hoo boy has there been a lot of discussion.
My own opinion: I think that a revised editions is a good thing. There is a nice simplicity at the core, but there's enough accumulated cruft on top that it's getting in the way of writers, GMs, and players as much as it is helping. (And some of the additions don't quite work with other additions, and so forth.) At that point, it's a good thing to redesign a cleaner, more integrated system that does nice things with all the accumulated cruft.
The preceding paragraph sounds much like my opinion of our current codebase. I don't think that's a coincidence.