that sounds great in theory but put it into practice: the pokemon would have to be put to sleep by your opponent (the choice item would lock you into rest if you tried that), you would have to waste two turns swapping out and back in again, and when your pokemon wakes up, there goes a third turn swapping out again, not to mention loosing a move slot to sleep talk in the hope that this happens to you. You are also not guaranteed the best move for your scenario. In short, there are too many risks for the payoff in this strategy