Add ability to have multiple +page.svelte for one route

Describe the problem

Imagine a typical social media platform, where unauthenticated users are greeted with a marketing site with signup/login on the root path /.
After the user has logged in, the root path typically shows the feed.

If you want to implement this behavior in sveltekit, at the moment your only option is to use if blocks in the / +page.svelte to conditionally show the marketing signup/login page or the authenticated social feed. With this approach you basically mingle two pages into one file and loose the ability to have different layouts or load functions.

Describe the proposed solution

It would be a lot cleaner if these two pages would have separate +page.svelte files.

With the file based routing one of the two pages would have to be declared as a subpath for example the feed page would be located in a /feed/+page.svelte

Now we'd need some kind of server hook similar to the existing reroute to tell the sveltekit router that the feed page is not to be shown as /feed in the url bar but as / based on the user session state.
If you use goto('/feed') this should also trigger the hook and show the feed under the root path.

Alternatives considered

No response

Importance

would make my life easier

Additional Information

No response

Start with SvelteKit's file-based routing, the existing reroute hook, and goto navigation. Examine how /feed/+page.svelte and the root +page.svelte are resolved for different session states. Done should allow separate page files to render at / based on authentication without changing the URL, including navigation through goto.