Whats the purpose of adding the pubkey to the URL when in most cases its available from the kind 1 note the URL was posted in?

Also its possible for multiple pubkeys to upload the same file, although this could easily be fixed by making each pubkey work in the URL

However the biggest missing piece here is the ability to re-upload your (or someone else's) files without modification. censorship resistance isn't going to work if you have to ask the original server first before you migrate