Ruby support in uWSGI is really solid, and it is more used than you can think of (As an example the biggest italian rubyonrails site run over it, and you will find a bunch of interesting blog posts about it combined with ruby). The main issue here is that we never pushed it in the community like we did with python and perl. Frankly i do no know why, maybe it has been a terrible error (taking in account that whoever tried it with ruby has been really excited)
According to that page, it doesn't support the most recent Ruby versions. That might not be accurate, though.