(Manas.Tech employee here)

Back when I joined Manas.Tech and learnt about Crystal, THE wow factor for me was the way `if` constraints optional types when you check it: https://crystal-lang.org/reference/1.5/syntax_and_semantics/...

That provides you the flexibility of having union types (variable may be `Thing1` or `Thing2`) for generic purposes, AND type-safetiness (is that a word?) when dealing with specific paths of your program that apply differently to some of the subtypes of the variable.

I think Swift and Kotlin support (some of?) that now. It was really new for me back in the day (around 2014?).

But that's from a coding point of view - not that much about niches, as you talk about.