If it's possible to create logical repos its possible to create clone channels from master repos.
With this information its possible to update some group of systems. For other apps it can by possible to import this logical information or to create this logical repos over xmlrpc.
Cobbler speaks yum (and now also apt, from JP's work) -- standard upstream tools. There is no such thing as "logical repos", "clone channels", or "logical information" in Cobbler, nor do I want there to be.
Today, if someone wants to snapshot a repo, they can simply copy a yum repo to a different directory (cp -a) and hardlink it, and make a new cobbler repo entry for the new one. Maybe later we'll teach "cobbler repo copy" to have the concept of making copies for you. That might be nice. If you want to compare repos, I believe that's repodiff.
--Michael