https://static.sched.com/hosted_files/icann83/5b/Rafaelle%20...
Quad9 (9.9.9.9) consumes this feed from U Twente of "just deleted" names, as most of them are malicious, and blocking them even if they are NOT malicious causes zero harm. Currently, this is only names that are very short-lived, so may not catch the longer intervals where names are deleted and become ghosts.
Another model using something similar would be to specifically clear those "just-deleted" name cached entries out of the recursive resolver, but that is expensive. Also, with blocking instead of removal it is possible to get high-level metrics on how often those are being abused where NXDOMAIN tracking is not measured in the same dimensions.
(disclaimer: I work for Quad9)