Yes I have, which is why if Diddy is shown, we will know if there is a Dixie tag team as well (unless theres a part of the mechanic where one could can be dead and the other alive)
In DKC, when you have both characters, you control one and the other mimics you, faded out in the background. There could be tag Out mechanics, throw mechanics, etc. They were featured in DKC games. Diddys side b, for example, could have the characters switch if the attack is successful (latching on to opponent) and you could follow up with attacks from Dixie.
Im not saying this is a guarantee, or even likely, but possible. If Sakurai wanted to do it in Brawl, he may want to finish the job in this game.