If I were you I'd still stick with Python ecosystem, just because you say you're comfortable with Python & Flask. When you come to Ruby right from Python 'it feels the same, but different'.

You won't lose anything if you stay with Python/Django stack without touching Ruby/Rails. I believe the number of jobs available for Django and Rails developers is more or less equal if we talk about that point specifically.

But if your goal is just self-education, then why not give Ruby a try?