Is it a temporary shortage, or is it that Korg no longer wants to offer their premium action at a sub-$1000 price, that is the question.
How does Korg's action compare with products from Roland, Kawai, Yamaha, and Casio? At what price do they offer a similar piano? I've never actually played a Korg, so I've no idea.
1. I think the Korg RH3 action is comparable
to the various Yamaha midrange actions (GH3, GH3X, NWX). Definitely much better than the GHS.
2. I have not played any of the Roland actions, but the PHA4 sure looks nice if the key actions photos are anything to go by.
3. The RH3 is definitely better than the mid 2000s Casio Scaled Hammer Action found in the CDP 13X/23X range. When I tried out the Tri-sensor Scaled Hammer Action II
from the Privia/Celviano range, I put it between the GHS and the GH3X.
That would suggest that the Korg RH3 is slightly better than the older Casio actions, but I cannot make that assertion with any amount of confidence as the Casio action was nice enough for me to consider buying a PX-160 for use as a midi-controller before I discovered the CDP-S and PX-S were launching soon.
4. I can't make a direct comparison between the Kawai RHIII (found in the CN27/37 and ES8) and the Korg RH3, but I suspect the Kawai action is somewhat better. I could only directly compare the ES110 with a CN37 and the difference there was substantial.
If I had a sub-$1000 budget and only cared about the action, models with the Korg RH3 and the Casio actions would be at the top of my list. And Roland, if available.
Around $2000 and you could probably ignore both Korg and Casio and concentrate on Yamaha, Kawai and Roland.
If the furniture, sound engine etc matters just as much as the action, the choice gets complicated real quick.