I'm not much of a fan of ditching plain text for binary, since it makes debugging more complex

I don't think this always holds true, like there was one time at work where an outgoing http request was failing in a strange way, and it took us hours to discover that the environment variable holding the URL in production contained a trailing newline, which the client library didn't pick up on. So this resulted in the following request:

POST /some/shit
HTTP/1.1
X-Some-Header: etc

some payload

If the length of the URL was known ahead of time, as would be typical with a binary protocol, the server would have known the newline was part of it, and handled it accordingly. It wouldn't be friendly as a plain text protocol, but it would make parsing the request very unambiguous and robust.

On the other hand, we see things like http/2 support in curl on Debian 12 being just broken, and the maintainer being too scared to merge the fixes from upstream due to http/2's complexity. So this cuts both ways, I suppose.

Oh, you can write a server that doesn't implement keepalive (while doing everything else 1.1) and still be 1.1-compliant? Well that's neat I suppose!

Yeah, you can just ignore the client's wish for keep-alive and send Connection: close, according to RFC 7230. I imagine this has to be terrible if the client attempts pipelining.

This might be a cursed opinion but I do actually want all websites to be root/path-agnostic. So if you wanna host Postmill for example but you already have a separate service running in port 80/443, and can't do it in a separate domain (which would require another host in this reality) or port which would have its own root, then I should be able to put it in like /postmill instead.

I believe Postmill supports this, but I haven't tested. I think a lot of devs just ignore the possibility you'd want to host something a subpath, unfortunately.