This is a great idea but I don't understand why not to extend something like swc to support svelte.

95% should be already there (maybe this does that? https://github.com/wuyudi/svelte-swc)

The repository linked in your comment seems quite empty.

(Not OP) That repo looks like a proof-of-concept which is linked to from an open issue in https://github.com/swc-project/swc which is apparently a "super-fast TypeScript / JavaScript compiler".