Interesting. Makes sense.
I used to have a Gen3 Glock 23. It was a good gun. A bit snappy, but not uncontrollable. Got slide bite at least once per range trip.
I've shot a Gen4 and Gen5 Glock 19 side-by-side a couple years ago at a rental range. Aside from the lack of finger grooves and the annoying half-moon cut on the Gen5 front strap, I couldn't really tell the difference. For me, I never even noticed the finger grooves on the 19/23 as they fit my hands perfectly, better than any other finger-grooved gun/grip I've tried.
I am curious about one thing. If the Gen3 Glocks are going to be produced for the CA market, will they be available elsewhere, or are they going to scale back production and limit distribution to CA? I would prefer the Gen3 to the Gen5 primarily because with the Gen3 I could still use the NY1/"-" connector trigger set-up I like. That option isn't available with the Gen5 guns, as far as I know. Not that I'm planning on getting one anytime soon, but I think at some point I'd like to add a Glock 19 to my collection.