RegexpVirtualURIMapping is a useful VirtualURImapping but is not site aware. It would be useful to be able to target a mapping to only apply to a specific site.

This would allow each site to map a specific url pattern (such as that created by RepositoryToUri mapping) to a different actual page.

In fact this is the usecase which drives the creation of this mapping:
We have two sites which should allow linking to a contentItem from a specific workspace: tours. RepositoryToUri mapping creates a url with the name of the workspace in the link.
Now we want to use VirtualURIMapping to forward the requests from these links to the different pages in the different sites which should display these tours.