I don't think it will work. As soon as it is implemented, people will be very nice in every game, but being nice doesn't mean someone will commend their behaviour. Negative behavior is really hard to forget, that's why you remeber to report other players after the game. On the other side, good behaviour is really easy to forget and it will be mistaken as just doing his job. People won't care about commending some one unless they earn something in return, like trading commendations, something Riot will try to spot and prevent.
I have played 200+ games of dota2 and I haven't give a single commendation to another player, besides my friends. I also have only a couple of commendations from my friends. Maybe I'm not nice enough to pubs to earn their respect...