Seems like most of the features you need are what mosh offers. I've been using it for a decade, probably, and it is pretty awesome for latent mobile connections (read as: throttled 2G @16kBit/s with interruptions).
> If you want to have 10 concurrent connections, you have to open 10 ports.
That is a problem in most environments.
Either you waste lots of traffic bandwidth because you have to have a session identifier or nonce in every packet, or you have to map sessions to ports in order to guarantee persistance when the client drops its connection.
Other ways of doing session handling will lead to an attack surface that can probably be used for DoS attacks.
Maybe I am missing something: How would you solve this, given the limitations of UDP and TCP?