I don't really grok what this means - WebAssembly, .NET, and the JVM are runtimes, how does Rust compiling to them lead to a future that doesn't require a runtime?
I'm speaking of the program itself not requiring a runtime. It can run on platforms where there is no runtime, like directly on POSIX.
And the fact that the program isn't tied to a specific runtime also would make it more compatible with other runtimes. You can't really run a JVM program on .NET, because the JVM and .NET have two totally separate universes of assumptions the runtime makes. When the program is runtime-agnostic, it can more easily be retargeted to different runtimes.