The problems described here seem like they could be solved by email clients, rather than abandoning the whole protocol.
It's a client UI and server configuration issue.
Email clients and servers could be configured to support instantaneous transmission, with a client UI that is presented in a thread like format (no, I'm not talking about thunderbird "threads", that's just mozilla wasting more of goggle's money).
This really _should_ replace SMS even before messaging apps. SMS is a seriously bad service-provider-dominated security nightmare.