I imagine, due to the inclusion of 'playing on more than one character at a time' on that answer, that they've received this question a lot indeed where a player has more than one character on one account and would like to play with them simultaneously. That's probably what they're referring to, I maybe guess.

I'm sure someone there has at least at some point thought about using real-money (micro transactions I guess people call it) in many ways, but I doubt they would ever allow characters to be traded. Not in this game.

But well, impossible is nothing. No one knows what the future will be like. ^^