[wtallis]

> but it also prevents you from dividing up a logical heirarchy into multiple behaviours (compression vs. not, block size, etc.).

Bind mounts can get around most of the limitations here, at the cost of polluting one directory with the canonical locations of all your special-purpose subvolumes. I think it's still awkward to simultaneously snapshot every subvolume that is mounted under a particular tree for incremental backup purposes.