Yes, and for anything that already compiles to JS, adding this as an additional target shouldn't be too much work.

However, for anything that doesn't already compile to JS, this is essentially the same amount of work as targeting regular JavaScript. In that case, the work might be better spent making it compile to WASM. But, that's not a hard and fast rule, it really depends on the situation. And, of course, it could always target both.

Sure, why not? The difference is that WASM is aiming for near native performance of code, while the binary JS would still be limited to JS performance.

Yes, but it would have access to DOM, GC, etc.

But that's what languages that compile to JavaScript support already today. The binary JS shouldn't prevent this behaviour if it is just a binary representation of a text version.