Sorry to be a pain, and with full recognition that I don't probably represent the majority, but I care about emoji reactions, reply support, ability to send & receive images and video, ability to see that video later, a reasonable set of access control features for group chats; reply-privately for group chat messages, and a dozen other things. And I care about not making someone download an app I've never used that talks the protocol, because I can't support them getting started. So a single cross platform UX is needed too before you can hope for traction.
Some of this is UX; some requires infra (eg. storing & forwarding media)
But to produce a "complete" messaging tool is harder than it looks and the protocol layer, while important, should not be the focus of discussion. There needs to be a holistic conversation that includes UX, infrastructure capabilities, branding, and network effects.