As a bronze player who feels he is lower than he should be (and is currently in promos to silver), this is a terrible idea. On the one hand, you can attribute toxicity to people feeling they're stuck where they are unjustly, but it's just that kind of behavior that they need to learn to control before they're ready at higher ranks. Even if they could keep up mechanically or with rotations and other things that just don't exist in bronze, they NEED to learn to control that toxicity, as that is what's keeping them from climbing.
In addition, removing the rank caps in combination with Dynamic Queue would be the ultimate way to make the boosting industry extremely profitable. The higher ranks would suddenly be inundated with people who don't belong there, people who paid to be boosted or were boosted by friends to a much higher rank than they deserve. The average rank of players would first shift up, then shift down because the people who deserve to be higher up would be losing games because of the boosted bronze players.