You won't see stuff on all devices or clients, unless the clients share with each other which might be in the plans though.
Also, peer to peer is not hiding behind a relay so people you DM with could see your IP, if that matters.  

 Doesn’t it mean ruining the whole point of nostr which is being interoperable and not centralized ? 

 Wouldn’t ruin the “whole” point, I think it would be usecase specific, notes would always need relays, calling, and maybe even DMs don’t really need relays. Solutions to problems often have a way of sidestepping politics of ideas. 

 Even less of an illusion for "global" 

 p2p is harder especially for offline and prevent ip exposure