Rat is correct in that will be something we're never going to see. I suppose there's a .01% chance or something absurd, but maybe not even that.
If they ever do it would be a sure sign that the game is on it's very last days and about to be shut down.
Simple thing is this: Plarium won't allow trading because why would someone buy $1000 worth of shards to *try* to get whichever champ when they could instead pay someone $100 to trade them that champ, and plarium wouldn't see a dime of it.