Well you know: some kind of "nostr neighboorhood protection" would be a cool idea :)
decentralized physical bitcoin network layer is also a high priority in my point of view.
nostranslator for weblate alt. is also interesting (my idea with someone els was: (backup)data stored in git repo. "contributions" made in dedicated app wich create templates based on user defined patterns. Easy to adjust to types of translation files or to check if contribution meets criteria for host while contributor can create offline.)
an international weather report system would be really cool I guess.