I think it will most likely be smaller devs and indies who use Rust for game dev initially. Once demand grows, hopefully there will be better cross platform support in the future. Thankfully Rust emits LLVM IR, so that will make expanding to more platforms like iOS, PS4 and Enscripten much easier. XB1 would still be an issue though... not much you can do about that though.

For me, Mac/Win/Linux/Android/iOS support is more than enough, and I think it will be enough to bootstrap the language into some level of industry acceptance. It depends on the project really, and how much the developer values console support over the benefits that a modern systems language like Rust provides.