How long until we get continuations in Java? Maybe another 10y? How long until we get TCO? Lets say 20y?

And in the end it will still not feel clean or as neat as other languages, that had this stuff for multiple decades.

None of those are a necessity, and they can be easily implemented in an additional layer (e.g. annotation processor if you really wanted to).

No language features above machine code are a "necessity". Java is not a "necessity". "OOP" is not a "necessity" either. Why don't we all work in C? Or maybe all in assembly language? Yet most of us are glad we can work at a higher level. Probably no single language feature is a "necessity", yet when they come together they make for higher level languages and elegant expression.

Hopefully never. There's a reason no primarily functional language ever became mainstream. The "elegant code" they allow is never as lovely as the zealots imagine