Let me rephrase a bit, and this is now my opinion not op's. The UX is the most important problem to solve. Sure making a secure federated chat app may be harder

Let me rephrase a bit, and this is now my opinion not op's. The UX is the most important problem to solve. Sure making a secure federated chat app may be harder in quantifiable sense, the structures are not really know. But for UX, honestly speaking I feel like nothing is known. We can copy WhatsApp interface, just like you can copy signal/WhatsApp architecture. But is that really what makes them successful?