What is the use case for this? Getting rid of the need to use svelte-preprocess when you use TypeScript and nothing else?

Yes, and also when using css preprocessors like scss and stylus. Typescript would be handled with Vite's own esbuild instance so it would replace the need for svelte-preprocess-esbuild. Css preprocessors config can be shared via the Vite config too.

There is still use cases for svelte-preprocess though, like the recent TypeScript improvements, or it's more advanced preprocessing for style tags.