It is definitely possible (though not trivial in many cases) to detach the language syntax from the language semantics, allowing multiple syntaxes for the same

It is definitely possible (though not trivial in many cases) to detach the language syntax from the language semantics, allowing multiple syntaxes for the same language semantics. But detaching the semantics from the runtime, something you do not describe above, would be a very different thing: the runtime is a /part/ of the language semantics, and while you can definitely create multiple languages that share a runtime (as the JVM languages do, for example), any decision about the shape of the runtime is going to involve tradeoffs in capabilities, so there will never be one runtime environment to rule them all. What's needed are means of easily communicating between runtime environments, which is of course what protocols are.