@yabapmatt I've heard a lot of arguments about this topic and I'm going to share my thoughts here for posterity.
I think giving people a somewhat level playing field based on their card levels is a good idea, so I can support the idea of bring back league level caps. However, I think most people aren't even concerned with the " as they existed in the past with separate leaderboards for each league" part and I think that is actually a turn off for many that could consider supporting this idea.
From the comments/questions/concerns I get regarding this topic, most people just don't like playing against higher level cards they can't afford or beat and feel it makes the game unfun. This is where I think Brawls and Tournaments really shine. Hopefully this information can help you make a decision on how to proceed.