One of the more frustrating aspects of some clients like Gajim is that you can be in a multiparty chat, but there's no way to tell why OMEMO isn't working. You're probably missing somebody's keys, but unless you go spelunking through debug logs you're never going to know. And good luck if one of the members of the memberlist rarely signs in, then you'll never get his key thus rendering OMEMO useless!
What I think is even more frustrating is that OMEMO is not required by default. I try to communicate with a group of people without WhatsApp, but I'm not in a position to tell them each which options to check, and what to look for. That's too much hassle for them. That's why I think Jabber/XMPP is lost.
Encryption must be on by default. Better if there is no option of unencrypted communication at all. Go get a debug build for that.
Receiving receipts and reading receipts are a must. It must be on by default. Communication always goes two ways. I had enough situations where one couldn't be sure if the other person has read an urgent info and whether the situation needed escalation.
Account information must be hidden, if the system is not decentralized. People don't want to remember account names and passwords. Get device specific keys, or whatever. Just hide it from the user, unless they want to look at it. People don't want to hear about servers.
