Pulp's Filters are great for filtering/black listing packages. However the Filter's "package list" accepts constructs such as regular expressions which implies variable matching.  
At the present time one has no way of knowing whether the package_list will filter the desired packages when a repository is being cloned with filters applied to it before actually doing the clone operation. 

We need an operation where One can either
a) pass a list of packages to a filter and have it return packages that would get blocked.
or
b) have a repo clone "simulate" operation which will actually simulate the clone with the filters applied and then return the list of blacklisted packages based in the filters.