These are some very good ideas. Going back to my Civilization days...you can build your empire tall or wide. I think if the ultimate goal is to have as many human players as possible then building wide should definitely be a big part of the plan, and to do that you need to incentivize the "middle class" as you so aptly describe it. I like your idea of the Champions League getting rewarded from outside sources. Of course, those sources need to be found and developed. Easier said than done. But if this truly is a game for the long haul, then that should already be a part of the thinking.
In the meantime, on the face of it, this proposal does seem like it will incentivize people to combine cards. How much? Who knows. But as @yabatmatt said, even combining to Level 2 or 3 could make a huge difference on both the rental market and the regular market. Hopefully the law of unintended consequences doesn't rear it's ugly head and cause any major problems.
As a final thought, do you think making cards rent for a 1 DEC minimum would do anything to get people/bots to buy more cards rather than rent? Just wondering...