Same Account Character Interactions

So I do have both Horde and Alliance toons and I wanted to be able for them to be able to mail one another. I know it is not possible at this time but would it be at another time in the future? Also, when going through Auction Houses in Goblin Towns (Gadgetzan, Booty Bay, etc) I cannot buy auctions that I have put up on one character (horde) to another character (alliance) with the same account. Is there a reason for this?

Cross faction mailing was enabled for premium accounts at the beginning but it was disabled long time ago and most likely isn't coming back.

You can't buy your own auctions. It just works that way. You need 2 accounts for that.