[What if] Character Change in-game

I was thinking of a system that allows players, during matches, to switch champions with each other, but only with those who are added to their friends list. Items, gold, runes and etc would be exchanged as well. It reminds me of a system that DotA has. The exchange could only be made once per match and under specific conditions. Who never thought of something like "if I was with Tristana in my friend's place ..."?