> While not an outright flaw, I also think it has become clear by now that it is highly suboptimal for "address" and "port" to be separate notions.

If we fixed that issue, what would be different? The operating system still needs to assign different addresses to different sockets. So now... we have 48-bit addresses, and instead of reserving one "address" and giving each socket a 16-bit port, we reserve a /32 block of 65536 addresses and give each socket its own address with a unique 16-bit suffix?