Yes, there definitely are other problems. For spam, you can have centralized blocklists that people can subscribe to. The iOS version of whatever would need it

Yes, there definitely are other problems. For spam, you can have centralized blocklists that people can subscribe to. The iOS version of whatever would need it anyway to follow the App Store guidelines. If you feel you're being censored, unsubscribe from the list. Alternatively (or in addition to that), have everyone publicly publish who they blocked, and then trust what your friends or friend of friends blocked. Network wide search is a problem, yes, but for chat (which I really want to be decentralized :( ) it doesn't matter too much. Monetization for content creators also doesn't matter for chat. So maybe I should rephrase my initial comment: Lack of NAT/Firewall bypass is the largest (and maybe only) problem needed to be solved for decentralized chat.