- Yes: https://github.com/sveltejs/svelte-loader

- Unsure

- Preact is essentially a lightweight implementation of React. As such, it requires a runtime, albeit an incredibly small one, to dynamically render HTML from JSX (Edit: Well, compiled JSX. Essentially hyperscript function calls.).

Svelte components compile at buildtime to pure es5, so you can just run it directly on the client without a runtime.

There are benefits and drawbacks to each method, but that's the gist of their main differences.