The ecosystem is great, but it has its own limitations. For example, to my knowledge Scala has not been able to implement tail recursion optimization, citing JVM limitations.
You're more optimistic than I am. And honestly proper TCO doesn't seem to be all that important to "regular" java programmers[1], it's just that it's crucial for $ALT_LANGUAGE implementers. (Where ALT_LANGUAGE has a functional flavor.)
[1] I'm guessing that this is the reason that it hasn't been prioritized... but who knows what complexity would rear its ugly head if one were to actually try to implement TCO on the JVM... I'd hazard a guess that it's 'highly non-trivial'.
BTW, there is a Scala compiler annotation that helps you check whether a function is tail-recursion optimized.
Scala supports local tail call optimization for a single function. A lot of FP languages support mutually recursive tail call optimizations, where two functions recursively call each other (common in FP). Scala (and no JVM language to my knowledge) cannot optimize this and so programmers have to resort to workarounds like Trampolines.
In contrast, LLVM IR and .NET CLR support it, allowing language compilers to use it. F# supports it and there's plans for C# to support it. It might be supported in the LLVM Scala target (Scala native) at some point in the future.