> Elixir is quite new (2015) and with every release it gains in maturity, and the ecosystem is growing.

One thing I really like is that it's considered mostly done. The community has the wisdom of not always trying to add new features and deprecating old ones. There's no 2.0 planned but that doesn't stop people from doing impressive work like Nx. I don't know about the ecosystem, but the language itself seem like a stable investment.