I guess you're seeing it from the service owners point of view, and in that case it doesn't really matter no? AFAIK, it's for the owners of the email to use the subaddressing, not for others to magically come up and use subaddressing.

So as long as you, the user and owner of an address, know that your domain supports/not supports it, you can use it.

I don't understand who would have to add any allow/blocklists?