First, I think the intention is very good. There are some problems with email that I don't know if they are possible to fix. Yes, JMAP [1] try to fix some of these problems for clients, but other flaws cannot be fixed without breaking backwards compatibility. Even unsuccesful, audacious experiments like that bring about discussions about what are the limits of current technology, what alternatives we have and what alternatives we can build.
Anyway, the best solution for asynchronous communication is still email. An incompatible solution would have to provide a compatibility layer for that. People refer Matrix here but I've always thought that, although many teams have adopted Matrix as a solution for general communication, it is a chat platform and not a replacement for asynchronous communication.
I just glanced over the site so I may sound repetitive: as a suggestion, I'd recommend adding some screenshots of client applications, diagrams explaning how mnm works, an explanation about federation and something that highlights differences to email.
[1] https://jmap.io