It's fairly new, but OMEMO was just officially published (now that there are free specs available to reference and everyone can be sure there won't be weird legal trouble later), and Conversations (an XMPP client for Android) has just started using a new Trust model (https://gultsch.de/trust.html). It's early days, but I can see this being a good compromise between security and ease of use (like Signal). We'll see.