Yes contacts, notes, your profile info, lists, application settings. Nostur already stores these locally, and has an export button for notes. I plan to add a toggle to sync to iCloud, and an option to publish to relays as well.
Discussion
I find it interesting, a doubt: what happens if over time I have a lot of data in Nostr that my space in iCloud is insufficient. Don’t you think we would have a problem there?
It’s mostly small text files, all my own data right now since the start of the year is less than 1 MB.
If you ever find a way to push the limits then I guess archive and purge could be an option.
You're right, I like that functionality of syncing with iCloud. We will see about space over time.