Yes, that's exactly the point. What I'm trying to do is:
1. Use Rust because it's fast.
2. Make REPLs universal, so we don't need separate REPLs for different languages.
3. And third—though not a new idea—is to create better abstractions, like allowing print statements without requiring a main function, and accessing variables without explicitly printing them.
That makes a lot of sense to me! I imagine that a lot of the logic you'll define will be fairly independent of the language itself, so you won't need to do quite as much work as if each one were implemented separately.
How do you download and manage the various language toolchains though? At least in my experience, the ease of doing this varies quite a bit by language and OS. Some distros have better package managers than others, and some of them don't have first-party ones at all. If I want to install Python on MacOS and haven't been using it enough to know which of the half dozen or so tools that are recommended by various people for it (or might have a sense of what to use but lack interest in learning the specifics of yet another tool for a language I need to do something fairly basic in), having a single tool that I'm already using for a bunch of other languages that I can also use for Python might be pretty nice.
