Ideally it would be good to have two ports, one for the main net, and one for the test net. However, in light of conservation only one may be granted. The question as to whether traffic could be multiplexed over a single port may be raised.

I'm sure it would be *possible*, but testnet and mainnet are entirely separate networks. Not only that, but the entire point of the testnet is separation. There is no logic to multiplexing them.

If conservation is an issue, I'd forgo the testnet port. We don't have a 'test ssh' or 'test mail server' port either, most people will just allocate a temporary number for those themselves.

In case the port is already in use, bitcoin can run on and announce any another port. There is no strict need for it to be 8333 (or 18333) at all.

There isn't even an argument for convenience. Most of the time, users don't specify nodes. And in the rare cases that they do they can specify a port as well.

If a whole slew of alt coins also tried to reserve ports, I suspect that may raise eyebrows.

That's somebody else's problem. Bitcoin is by far the most well-known of the 'coins' so it may be considered realistic to allocate one or two ports for it. Or not, in which case the altcoins can forget it too.

Regards,

Wladimir