This comment is regarding the creation of the default dict defining where the different folders are located:

./python/vyos/configsession.py:# XXX: maybe it's better to do via a systemd environment file

The code could instead parse a systemd environment file (which should also be used by systemd).

Further down the line, this environment file could be generated and also used to configure the shell.
As a first step, the hardcoding could be removed from the code and a systemd file parsed and used by daemons.