Sub shop content overrides

As a sub shop user I would like to have ability to redefine CMS elements and pages inherited from the master shop.

Some ideas:
ContentServiceFacade - per sub shop overrides? need to separate categories and content first
on content object we need a shopId/shop code for which it was created
need to change the uniqueness of URI to code+uri
change resolving of URI to content to include URI bit (need to resolve with fallback)