Does this now work reliably even when starting from within Nautilus (see 100% cpu with every scroll in LibreOffice - #29 by equbes)?
I also see that discussion in Make qubes-session inherit the systemd user session variables. by Rudd-O · Pull Request #151 · QubesOS/qubes-gui-agent-linux · GitHub resulted in you blogging about /etc/environment.d. How is this different from what you just recommended @Rudd-O?