So, you can now search for 'num URLs'. You will find it under a new stub, 'system:urls', at the bottom of the normal system predicate list (where 'system:known urls' has also moved). This first version is simple--it counts all URLs, regardless of how important, but I can see a future version having the ability to scan by 'post URLs' or specific URL classes. Give it a go and let me know if you run into any trouble!