As a software dev and open source contributor: stay the course, then! I'll take open source software over a union 10 times out of 10. I get paid so well for what I do that it's silly, and I love spending my time doing the stuff I like. I've been a union member in other fields, it's not an experience I'd like to repeat.

I seriously doubt anybody is contributing to open source for status & seniority. Respect, maybe. The status & seniority people become managers; as the old joke goes, that's the best way to get them out of the workforce.