I use(d) a VM for testing purposes and things were working quite well unti I added Plasma. So, if I take this to real hardware I might split up the QT and GTK based DEs in separate distros
Yeah I agree, that would be the best, but also slightly annoying. No more common shell history or web history and stuff like that.
I haven't had any major breakage using both Gnome and Plasma myself. It works fine. But it's annoying to see Gnome apps in the Plasma menus (when typing program names).
Gnome and Plasma is the absolute worst example. Normally either GNOME or Plasma take over all icons and everything looks messed up. For me even after installing just Dolphin on GNOME everything was messed up.