TYPO3 Core

The StaticRouteResolver can handle "staticText" and "uri".

I suggest a new type being a class->method()

Reason for this:

The PSR middleware returns a Response once it's processed. The Request object is present and the current site including it's configuration.

I see some great use case for static routes like

/blog
/news

and similar, that can respond to routes that a editor doesn't need to create. The class can then render a typoscript object, alternative template or similar.

Alternatively, this issue can be closed with the descission of saying "you can implement such PSR yourself and should not be a core thing" - I will completely respect that descission.