Comment # 18 on bug 1071224 from Franck Bui

Sorry for the delay...

Letting tmp.mount still accessible is pretty dangerous (even if basic.target
won't pull it in) because there are several other ways to activate it
implicitly: for example when a unit is using private /tmp.

So the only safe way I can see would be to mask the unit by default during the
installation if no entry for /tmp is created in fstab by the installer.

Regarding the upgrade path, we could mask tmp.mount if no tmp.mount is
currently active and restore /usr/lib/systemd/system/tmp.mount if not present.
Otherwise if a tmp.mount unit is active, simply restoring the one shipped by
udev should be enough.