Promos should be played against players of the rank you're going to, regardless of MMR
It doesn't seem fair to me that if you're a Silver 4 player with Gold 2 MMR, you have to play your Silver 3 promos against other Gold players. Meanwhile a Silver 4 player with Silver 3 MMR will play their promos against other Silvers. The fact that LP gains/losses are weighted based on MMR doesn't matter when you have to win 2/3 or 3/5 games to go up.
