Long time Pentax user, and I'll still use my debayered K-1 Monochrome (very few of them exist) and K3-III. They serve a different purpose than my new-to-me GFX100S will.
I won't pretend it's not expensive to move into the GFX system, but between very good adapted Pentax 67 and 645 glass I own, and two Fuji lenses, the GF 21 and 50, I can make it work without upsetting the wife too much.
There's a lot to learn and this looks like the place to be to discover and share.