What's "possible" and what's available and tested in production right now are two very different things. These kinds of ports take at least a year to get over the initial troubles and become usable and then you're at least that time away from a decent size of community libraries to spring up for the mentioned platforms.

By that time Rust will also mature enough and webasm will land so Rust will probably be a better candidate (since it's OSS and developed by a browser company that needs to run on as many platforms as possible they have much better incentives to maintain ports than Apple).

Also in that time C++ will probably get modules working on clang and many c++17 features.

And you might see Xamarin merge into CoreCLR and rolled up into VS integration.

A lot of things are possible - but what's available right now is C++ on every platform and not much else.