There have been some updates on the linked CA/B ballot in Will six day certificates allow rdns zones?, so I wanted to update the topic but it was autolocked...
tl;dr
[...] we will not move forward with this ballot as-is, as there is value in allowing issuance for DoH/DoT nameservers under .arpa and do not want to hamper those efforts. Our current thinking is that ballot will be scaled down to prohibiting wildcards under .arpa, but we can certainly discuss.
It seems that individuals within the CA/B community acknowledge valid use cases for issuing for arpa domains.
Would LE be open to reconsidering the arpa policy at some point, based on this? It seems like it could be a nice additional feature for six-day certs after IP issuance is rolled out.