I'd like to offer up a suggestion that I believe would be VERY beneficial.
On the WHMCS public website, we have whmcs.com/members/verifydomain.php , which allows us to license check a domain to see if they are using a legit License and if not report it.... What I think would be very beneficial, is for developers who use the License Addon would be to use the License Tandem along with the WHMCS License Checker maybe through an API. In my case, I've had alot of people who want to use the software I develop for WHMCS. We have a policy on our site, and it's that a LEGAL WHMCS LICENSE is REQUIRED for use, and we have the right to suspend a license if we find that their copy of WHMCS is not legal.
This is what I'm proposing.... How about an API to check with the public Verification portal on WHMCS to see if a license is legal, and if it is not.... do three things...
1. Do not allow the person to use or install said addon/software
2. Report said domain that is not authorized for use directly to WHMCS
3. Set said Clients' account to Inactive (likely through a hook) to prevent them from logging on, and then perhaps ban their email / ip.
Speaking of which, I may need to open up another idea, but I do believe on the ban of an IP, their should be an indefinite button or checkbox instead of setting a date :)