It's a bit timid of them to start from C#

Agreed.

Sure, an ML with no or optional garbage collection would be rather uncharted territory

There is MLkit [1] (one of the inspirations for Rust), so it's definitely not uncharted. I don't think it broke free from GC, but it was a step in that direction.

[1] http://www.itu.dk/research/mlkit/index.php/Main_Page