> It's very easy to fuck up the implicit state tied to the connection, and this requires discipline to get right. It's very easy to ship unreliable software that then has issues based on the connection.

I agree with this and it's why I believe that Phoenix LiveView is the best solution to this problem. The programming model and tooling that you get with the BEAM (along with things Phoenix provides like PubSub) are the best there is to manage this complexity.