Hey @beidl,
It sounds a PDK should fit under our supported categories to gran classic confinement, but based on the reasons you have provided, I would like to ask some further questions, since:
If I followed your related doc properly, you could bundle qemu-virgil the same way other snaps like sosumi are already doing while keeping under strict confinement.
You could plug the mount-observe interface, although you need to see if the accesses provided by the interface are enough for your needs.
You can plug docker as well as the kvm.
So, does ubports-pdk require access to files on the system (such as the usual case of IDEs requiring access to headers/compilers) or any other requirement which are not provided by some of the supported interfaces?