There are multiple reasons why we cannot play with friends in ranked at all. One, no one likes a rofl pub stomp. Two, joining friends who are well below or above your skill rank is a problem. It'll defeat the purpose of the ranks. Three, even if you limit everyone so that they can only join their friends in the same letter rank, this can easily lead to people throwing matches just to rank down to play with their friends.
Sadly, yolo solo queue also has their problems, but so long as you can win more matches than you lose, you should be able to rise in ranks fairly easily. In August, you will be able to form premade teams to go up against other premade teams, or you can create a private lobby and play against whoever you want.