Exactly, I think this would be a great platform for practicing builds or strategies at a competitive level.
And you have to realize there is a subtle but really important difference between this queue and Normal queue: You are matched for the game based on an independent reference. When you queue for a Normal game or a Ranked game, the outcome immediately changes the skill level of your next match. With this queue, you are continuously matched with players at your current Ranked MMR. So, although you could say this queue would end up being flooded with just as many trolls/unbalanced players as Normal, that problem is mitigated somewhat by the independent reference. When those trolls or players who don't fit in your skill level raise or lower their MMR they would no longer be paired with you. And on the other hand, there are always new players entering your match pool. The big difference is that you remain "stationary" on the ladder while everyone else shifts around you, allowing you a better chance to understand exactly how games at that skill level are played out.
You could then also say that everyone would just be stationary on the ladder, but two things should mitigate that. The first is rating decay from not participating in ranked games. The other is the fact that players using this queue should be competitive by nature and enjoy ranking. So this queue would serve as a temporary respite/training ground for players in new divisions.