Key rotation
Key rotation is useful for security reasons, but I don’t think it’s necessary here because it’s only used for verifying one’s identity. It’s no different (to me) than Nostr or a cryptocurrency. You change your key, you change your identity.
It makes maintaining a feed more complicated.
This is an additional step that you’d have to perform, but I definitely wouldn’t want to require it for compatibility reasons. I don’t see it as any more complicated than computing twt hashes for each post, which already requires you to have a non-trivial client application.
Instead, maybe…allow old urls to be rotated out?
That could absolutely work and might be a better solution than signatures.
HTTPS is supposed to do [verification] anyway.
TLS provides verification that nobody is tampering with or snooping on your connection to a server. It doesn’t, for example, verify that a file downloaded from server A is from the same entity as the one from server B.
feed locations [being] URLs gives some flexibility
It does give flexibility, but perhaps we should have made them URIs instead for even more flexibility. Then, you could use a tag URI, urn:uuid:*, or a regular old URL if you wanted to. The spec seems to indicate that the url tag should be a working URL that clients can use to find a copy of the feed, optionally at multiple locations. I’m not very familiar with IP{F,N}S but if it ensures you own an identifier forever and that identifier points to a current copy of your feed, it could be a great way to fix it on an individual basis without breaking any specs :)