You can use Mailinator to do this already, you can see all of their inboxes on their website and you can use all of their domains to bypass domain restrictions. For example I might use somethingsilly@bobmail.info and it will be redirected to https://www.mailinator.com/v3/index.jsp?zone=public&query=so...
but the list of mailinator domains is easily looked up and blacklisted by most major sites. the op's insight is that sites won't blacklist gmail
Why would you blacklist gmail.com when you can blacklist 'GuerillaClick@gmail.com'?