Honda hasn’t really pushed the CR250 platform. They wanted it because the tooling for the old cR125 engines is wearing out (it wasn’t designed to build engines for 15 straight years), but the big organizers didn’t like the idea.
Lots of people on here hate the idea of switching to 4-stroke. I think it’s a combination of basic fear of change (though everyone says it’s fear of over-revs) and vendors fearing the fact that it has the potential to be much more reliable and potentially puts them out of the tuning business. The over-rev issue can potentially be solved with a slipper clutch, but that does add more $ to the initial investment.
If it does ever happen, the new Yamaha 250 motor is the way to go, not the Honda motor. The Yamaha HP is roughly on par with a KZ motor plus the intake and exhaust are correctly positioned for a kart setup (unlike any of the Honda engines). As far as I can tell though, Yamaha doesn’t sell the engines by themselves.