I’ve tried to but it’s hard to get a RoR job from another tech unless I took a big pay cut. What is so special about GitLab, can another company offer you what you want?
They pay based on local rates. For me, this is a big no. I don't think they are a company worth changing your stack for.
But going back to your question, this is a hard one... Unfortunately, I guess most companies look for experience in a specific framework, not even in a language in senior roles. Probably you would have to find some company and consider pay cut/start yours with the new stack. I think smaller companies may be less picky about your stack. You could also look for team lead roles and practice new stack while leading a team. Sometimes companies let you introduce a new stack, but it has to have a good reason. If you work with django I see no reason for rails.
I'm not "married" with the idea of working there, as a matter of fact I'm already on the interview process with another company (remote too).