Just seen this announcement in the v252 changelog:
"We intend to remove support for split-usr (/usr mounted separately
during boot) ..."
How does this align with support for separate /usr/ with dm-verity ?
For example, this will affect nspawn. See "man 1 systemd-nspawn" and
"--root-hash=" where in respect of /usr/ it says:
"Note that this configures the root hash for the root file system. Disk
images may also contain separate file systems for the /usr/ hierarchy,
which may be Verity protected as well. The root hash for this protection
may be configured via the "user.verity.usrhash" extended file attribute
or via a .usrhash file adjacent to the disk image, following the same
format and logic as for the root hash for the root file system described
here."
