Was? Last I heard, Dotty is ongoing and will transition into Scala 3.
I like to think of Scala as the C++ of the JVM world. It's a complex language with a lot of features, but it can be extremely powerful if you know what idioms to use and where to use them. For example, template abuse in C++ is akin to implicit abuse in Scala.
Maybe this is something that helped grow Go's popularity by being simpler ? (I don't know, just wondering)
But, on the other hand, a balance has to be found if Rust ever want to be widely adopted. Let's be honest 2s here, Rust is already hard enough to learn for the average developer, adding higher order function on top of that will not help adoption.
IMHO, right now Rust the just enough amount of complexity to still be interesting to the majority. It really depends on who Rust want to target in the long run.
There was functional extremism in Tony Morris and his scalaz pet project, but Scala was already doomed.
Of course, these are all things Rust has seemed to avoid and hopefully continues to avoid.