rolling is looking good so far -- hasn't broken badly, and has quite a few nice updates we don't want to bother 4.0 users with.
But I'm a bit concerned about minor updates that get pushed into cooker not making it to rolling (even though rolling is where in the end releases will happen), probably because people [including myself, got to get into it] tend to forget about the small updates once they're there. The auto-updater also never pushes stuff to rolling.
I wonder if we should reverse the logic here a bit: Right now, we push stuff from cooker to rolling/testing manually.
It may be better to have a way to manually mark packages that are not ready yet (e.g. toolchain updates that need more extensive testing) and automatically build everything not marked that way in rolling after a couple of days.
Keeping cooker and rolling separate is probably necessary, because for some things they will diverge A LOT at some point (imagine the Qt 5 -> Qt 6 transition that will likely happen next year... Got to get cooker to Qt6/Plasma6 quickly while keeping rolling stable).