GameCube Serial Port 2

[Jasoco]

What is the Serial Port 2 on the bottom of the GameCube for?

There are three ports on the GCN bottom. Ext. Port 1 is for the Game Boy Player, Serial Port 1 is for the Modem/BBA, what is Serial Port 2 supposed to be for?

Anything released anywhere? Can it be hacked by outsiders? Is it planned to have a purpose, or did Nintendo realize that they would eventually need a free port open so that it didn't feel inferior to the previous three systems who also had a port that was never used. (Except in Japan.)

Curious. (It is the one with the rounded side access hole as opposed to the Modem/BBA which is square.)

[tholly]

I personally don't know of anything that it is used for, but I would love to see something be made by Nintendo that takes advantage of this add-on port.