It's cool that SSH is getting some love but I'm a little sad they're not being a little more ambitious with regard to new features, considering it seems like they're more or less creating a new thing. Looks like they're going to support connection migration but it would be cool (to me anyway) if they supported some of the roaming/intermittent connectivity of Mosh[1]. 1: https://mosh.org/
AIUI connection migration (as well as multipath handling) is a QUIC feature. And how would that roaming feature differ from "built-in tmux"? I'm not sure the built-in part there would really be an advantage…
Mosh is like vnc or rdp for terminal contents: natively variable frame rate and somewhat adaptive predictive local echo for reducing latency perception; think client side cursor handling with vnc or with rdp I'd even assume there might be capability for client-side text echo rendering.
If you haven't tried mosh in situations with a mobile device that have you experience connection changes during usage, you don't know just how much better it is than "mere tmux over ssh".
I honestly don't know of a more resilient protocol than mosh that's in regular usage, other than possibly link-layer 802.11n aka "the Wi-Fi that got these 150 Mbit and those 300 Mbit and some 450 Mbit speed claims advertised onto the marker", where link-layer retransmissions and adaptive negotiation of coding parameters and actively-multipath-exploiting MIMO-OFDM (and AES crypto from WPA2) combine for a setup that hides radio interference to not be visible to higher level protocols beyond the unavoidable jitter of the retransmissions and varying throughput potentials from varying radio conditions.
Oh, I think when viewed regarding computers not the congestion control schemes adjusting the individual connection speeds, there'd also be BitTorrent with DHT and PEX that only needs an infohash: with 160 bits of hash a client seeded into the (mainline) DHT swarm can go and retrieve a (folder of) files from an infohash-specific swarm that's at least partially connected to the DHT (PEX takes care of broadening the connectivity among those that care about the specific infohash).
In the realm of digital coding schemes that are widely used but aren't of the "transmission" variety, there's also Redbook CD audio that starts off easy with lossless error correction, followed by perceptually effective lossy interpolation to cover severe scratches to the disc's surface.