Another upside is that if you use a less-common language, there is _not_ a library or package for everything just yet... so sometimes, that creates the opportunity to work on open source at your day job!
Some people will say that this is a downside, because you can't build new things or ship new features as quickly… But I suppose that it comes down to what you want to get out of your career, and what your goals are.
If you are careful and diligent, you can find a way to get paid to solve problems within the domain of your interests. It might take a few years of study on your own time, but I pulled it off; and if I can pull it off, that means that just about anybody can!
Plus, learning new stuff is fun, and I would not have spent the time that I did learning the things that I have learned, if I didn't feel like it was worth it for its own sake.
