To use it, you need a valid certificate for the connection to the server which has a hostname that does get broadcast in readable form. For companies like Cloudflare, Azure, and Google, this isn't really an issue, because they can just use the name of their proxies.
For smaller sites, often not hosting more than one or two domains, there is hardly a non-distinct hostname available.
With IP certificates, the outer TLS connection can just use the IP address in its readable SNI field and encrypt the actual hostname for the real connection. You no longer need to be a third party proxying other people's content for ECH to have a useful effect.
Even if it did work, the privacy value of hiding the SNI is pretty minimal for an IP address that hosts only a couple domains, as there are plenty of databases that let you look up an IP address to determine what domain names point there - e.g. https://bgp.tools/prefix/18.220.0.0/14#dns
> In verifying the client-facing server certificate, the client MUST interpret the public name as a DNS-based reference identity [RFC6125]. Clients that incorporate DNS names and IP addresses into the same syntax (e.g. Section 7.4 of [RFC3986] and [WHATWG-IPV4]) MUST reject names that would be interpreted as IPv4 addresses.
To be pedantic for a moment, ARIN etc. are registries.
The registrar is your ISP, cloud provider etc.
You can get a PI (Provider Independent) allocation for yourself, usually with the assistance of a sponsoring registrar. Which is a nice compromise way of cutting out the middleman without becoming a registrar yourself.
The biggest modern-era reason is direct access to update your RPKI entries.
But this only matters if you are doing stuff that makes direct access worthwhile.
If your setup is mostly "set and forget" then you should just accept the lag associated with needing to open a ticket with your sponsor to update the RPKI.
Actually the main benefit is no dependency on DNS (booth direct and root).
IP is a simple primitive, i.e. "is it routable or not ?".
1) How to secure routing information: some says RPKI, some argues that's not enough and are experimenting with something like SCION (https://docs.scion.org/en/latest/)
2) Principal-Agent problem: jabber.ru's hijack relied on (presumably) Hetzner being forced to do it by German law agents based on the powers provided under the German Telecommunications Act (TKG)
Part of the issue with RPKI is its taking time to fully deploy. Not as glacial as IPv6 but slower than it should be.
If there was 100% coverage then RPKI would have a good effect.
There's also this little thing called DNS over TLS and DNS over HTTPS that you might have heard of ? ;)
Erm ? Do I have to spell out that I was pointing out that there was more than the "ephemeral services" that were being guessed at that could take advantage of IP certs ?
VBA et al succeeded because they enabled workers to move forward on things they would otherwise be blocked on organizationally
Also - not seeing this kind of thing could be considered a gap in your vision. When outsiders accuse SV of living in a high-tech ivory tower, blind to the realities of more common folk, this is the kind of thing they refer to.