Yeah I had thought that C# was basically Microsoft's version of Java, GC'd throughout. But it's fine, I'm not particularly more excited by it now than I was before (i.e. unexcited). I'm not even excited by Rust, but maybe I'm missing something. I think it's fine to use GC for most things, and program carefully in a non-allocating style when you have to, using verification tools as well.
A classic: http://james-iry.blogspot.com/2009/05/brief-incomplete-and-mostly-wrong.html
It sounds like he uses Rust and has some issues with it. IDK about green threads but Ada has had tasks (implemented in gnat with posix threads) from the beginning. If you pin a CPU core to a task and don't use gc in it, that can handle your realtime stuff. Or these days, it's becoming more common to use an fpga for cycle level timing control.
Note that traditional Forth cooperative multitaskers used a few hundred bytes of code or even less. This stuff doesn't have to be bloaty.
Added: I've also seen a Boehm-style conservative GC in a few hundred lines of Forth. Using something like that in Rust could work nicely for lots of things.
Anyway, you can have a soft realtime gc with pauses in the low milliseconds (Erlang has that). That's OOMs lower than most internet ping times, so plenty fast enough for web servers. Which are all full of JS bloat now regardless.