Would the concept of client side relays make sense for some use cases?
I'm mostly thinking P2P DM's, but maybe there'd be others (but keeping in mind that most clients won't want the bandwidth costs of running a 100% public relay).
I guess nostr:npub1xtscya34g58tk0z605fvr788k263gsu6cy9x0mhnm87echrgufzsevkk5s's new LMDB-backed database for events would be a nice building block for this...