We're almost ready to issue certificates for IP address SANs from Let's Encrypt's production environment. They'll only be available under the shortlived profile (which has a 6-day validity period), and that profile will remain allowlist-only for a while.
Please note: We have more work to do before we're ready to launch this feature for the public. We don't yet have a timeline, and aren't ready to accept allowlist requests.
Here's a sample staging certificate, and a site using it:
Please speak up if you see anything interesting, weird, or wrong!
I think I already found a bug in Firefox's display of IP address SANs; BZ #1973855.