Is it niche? Scala is arguably the single most successful functional language. It interoperates with the whole JVM ecosystem. It's probably the #3 JVM language after Java and Kotlin.
Spark is Scala, Twitter was (is?) Scala https://sysgears.com/articles/how-and-why-twitter-uses-scala...
> Scala is arguably the single most successful functional language.
That would be Javascript.
Anything that runs on JVM should not be invested in.
Scala was niche (but of course, you need to define niche first) and its market share has shrunk further in the last decade.