it is not GDPR-specific. It can just wait over an inbox and offer to delete accounts on any service that doesn’t communicate with you often.
Having said that, it takes lotsa work to maintain the proper procedures of deleting an account on all these services up-to-date, and even more work if there is any automation. The need, on the other hand, is only occasional, and in the “vitamin” area. Not gonna fly as a business, IMHO.
It could indeed be a lead to another service, because it has a chance to insert its own link into pretty much any email in the inbox. However, what that service could be? What can be sold to a person in the moment of solemn recognition “man, Internet knows too much about me”? Well, maybe VPN service or something like that.