because, some registrars have the reservation feature for domains, the idea is to add this functionality of "reserve domain" at specified registrar for specified days.
how I see this in deal. Customer make a new domain order. At the time when invoice are created, whmcs will send, using defined by module, RESERVE command to registrar, and will set for domain "status = RESERVED" , also will set next due date for XX days specified in "Domain Registrars" (picture 1)
if order is payed in time, the whmcs will proceed wuth domain registration,
else , status will be automatically set to changed to CANCELED.