As a Ruby dev on the hiring market until recently Ruby seems to be in kind of the same spot as Perl some time ago: many new/existing Ruby/Rails projects are around, so it's kind of mainstream but not as much as PHP/Node/Java/whatever is which means less job offers, yet not quite niche neither, and there seems to be kind of a slight lack of Ruby devs around, and it can act as a differentiator, even for non-Ruby jobs. There's quite an interesting market dynamic at play here.