Hey!! ---I will surely integrate Gumroad as a payment moduel for WHMCS----------
I am WHMCS expert having 6 years of job experience in:-
-whmcs server modules development, WHMCS and WHMCS addons-modules development, whmcs theme customization , Whmcs payment gateway modules, whmcs re-seller modules development, whmcs domain registrar, etc.
Looking forward to your available revert and i will be there to help you out in the best possible way.
Thanks!!