This "Delist" feature should have been there since iMessage launch. I mean no one at Apple asked themselves "What happens if someone didn't disable iMessage before erasing their iPhone and no longer have it?". The other issue was disabling iMessage before erasing did not always work (personal experience since I experience this bug). The other major issue was that Apple didn't have a solution for three years for anyone experiencing this issue.
11/9/14 at 9:51pm