What do we have to use other than npubs? dont we need a persistant identified somewhere, somehow?
Nprofiles. It's the same as the npub, but includes the person's main relays in the code so that apps can find their info quickly.
Do they change if i change my main relays? I guess can i still share an old nprofile with an old relay i dont use anymore?
You will have to keep changing it as you move relays. All old posts will have your old nprofiles and thus link to your old relays. But apps should be smart enough to track relay hint changes and only use the latest ones.
Yeah, but if I put my nprofile in an article, or someone mentinos me, 5 years later its not useful, or am i not understanding this correctly?
They need to update your relay when creating the nprofile. Apps shouldn't just blindly copy-paste the address without checking if the your/your post is still there.
The npub has a stable checksum-like thing at the end that can be quickly eyed and checks the full npub, right? That was the entire point of bech32 and where the full value of npubs reside to me.
True. But what's the point of having that there if in the text or when sharing links around everyone is just using nprofiles? You don't need checksums on the app's internal stuff. Checksums are only useful if users can play with the address and we are making all users play with nprofiles instead of npubs.