Isolating processes from the specifics of the system they're running on is a key feature of the namespace-based model; it seems weird to call it a "side effect only". We should keep in mind that CRIU itself is still a fairly new feature that's only entered mainline recently, and the kernel already has plenty of ways to "make up" more virtual resources that are effectively controlled by userspace. While it may be true that these things are largely ad hoc for now, it's not clear that this will be an obstacle in the future,
I can talk about namespaces in HPC distributed systems, and they don't look anything like Plan 9 to me. They make life harder in various respects, and even dangerous with Linux features that don't take them into account (like at least one of the "zero-copy" add-on modules used by MPI shared memory implementations).
Isolating processes from the specifics of the system they're running on is a key feature of the namespace-based model; it seems weird to call it a "side effect only". We should keep in mind that CRIU itself is still a fairly new feature that's only entered mainline recently, and the kernel already has plenty of ways to "make up" more virtual resources that are effectively controlled by userspace. While it may be true that these things are largely ad hoc for now, it's not clear that this will be an obstacle in the future,