hm, can you point me at an email provider who provides free SMTP/IMAP/webmail or XMPP hosting for custom domains? I may be missing something, but I can't think of one...
The model is that you can try it out on the matrix.org server via riot.im or something, and then run your own if you like what you see :)
What does SMTP/IMAP have to do with this? We're talking about early adopters of an unused technology. In my 2016, getting into email is far form being an early adopter.
Sure, I can rent a server and set up my own, but that's a huge commitment to "try out" a protocol which non of my acquaintances uses yet.