Just wondering, in Arch you can set packages to be ignored.
The idea is once Plasma becomes 9.5 it will be fixed and stable before 10 comes out. If I want to freeze this state until 10 is stable again, how would I do this?
Yes set the package on hold in synaptic. It has an option for that. Like I said plasma-desktop and plasma-desktop-data are the most important ones to set on hold.