Im a huge fan of matrix and use it daily. Just to make that clear upfront. If you read HN you should use it.
I don't think it's ready for non-technical people. The federation part still causes issues. Occassionally messages get stuck etc. I would not feel comfortable telling my mom to download element to text me.
I know such things are possible (it works for me) but many people get themselves in a horrible mess.
But yes the client validation and key exchange is something non technical users don't grok :( Even though they've clearly spent a lot of time making it as easy as possible.
Also since the protocol is http, a friend of mine lets his servers send him notifications about cronjobs by just curling an endpoint. Lots of things you can do with it.