We do not allocate each physical host a /64; we (usually) allocate each network segment (broadcast domain) a /64. Of course, for p2p use cases that ends up with

We do not allocate each physical host a /64; we (usually) allocate each network segment (broadcast domain) a /64. Of course, for p2p use cases that ends up with a single-host network. Most of that address space is used to allow for stateless autoconfig, though. It would be certainly possible to fit in port multiplexing, but you'd have to make a trade-off in increasing collision risk, depending on how you do it. Or go back to static addresses or DHCPv6.