AFAIK, GDPR doesn't tell you there need to be an automated way to delete the data. If people can send you a mail with the request and you manually delete it, that's also fine. So if no one will use it, you basically don't have to do anything and be compliant (to this specific GDPR rule).
Sure, but if people use your service and some 0.01% of them might send a request just as a matter of principle once GDPR kicks in, then it's quite plausible that the cost efficient way to handle this is to have an automated solution rather than a manual process that doesn't scale.
From what I understand, as long as you can say there's a process in place (and could actually follow it) then you're compliant with the GDPR.