Why is this needed?

I'm writing a plugin to do SSR based on a route, for that I need to parse the SFC file and build a script similar to what vite does. But vite relies on the middleware and the request path to retrieve the cached files or to parse a new file.

Being able to access the internals would be really useful.

For consistency's sake, I think we either expose all compileSFC* methods or we expose none of them. However, making them public means we can't treat them as internals and freely tweak arguments anymore. They are also assuming to be only used in the dev-server, so it may at some time expect a Koa context - which would make them unusable elsewhere. I think for now it's safer to just copy-paste the logic in your plugin until it's more stable.

Agreed, in my case I only need the Style, the others I basically copied the logic over.

Is the rewriteImports good to expose?

Yeah, rewriteImports is probably safe, although I'd consider it semi-internal for now. You should be prepared if it breaks ;)