When I was bootstrapping a new system I had a lot of blockers when I selected systemd - I ended up setting systemd USE=-policykit I found that that Gnome would crash every time the user menu was clicked (the top right menu - I'm new to Gnome) I managed to fix this by compiling systemd with USE=policykit Can we update the gnome-shell ebuilds to require this
I just wanted to make it clear that only systemd had -policykit
What exact error (or backtrace) were you getting?