There is nothing more boring than have a competition that allows 15 teams to be permanent members. It maybe exciting for year or two maybe, but then the interest would dwindle, because it is the same s**t again and again. Which means that the organizers would need to do things to make it interesting for the audience, especially the on screen audience who generate big revenue. Which means bringing "packaged entertainment" to the audience.
Actual football, though not in the second place, would just be only one part of the "entertainment package" to be put out there. There will be so much drama beyond that.
By packaged entertaining do you mean that the overall goal is to throw in commercials in the NFL? It's a valid concern, but I haven't heard that mentioned anywhere. I just don't know if it's necessary/something you would do, as long as the money keeps flowing in from revenues, and the goal is to make a more entertaining format than Champions League.
However I agree, it'll be less versatile that's for sure. The money will only go to the big clubs over a period of years, so the lesser clubs like Leicester will generate less money and have a tough time to compete in the long run, effectively making the gap between the 15/20 and the rest enormously big. It would probably also make the national leagues quite boring, as the gap of quality will continue to spread into that one.