Now that we are talking about CL (for different reasons) I will do ma suggestion, based in a system semi-real (LOL).

As we know the actual rule, divide teams in 4 POTS, 1st with the winner + the 7 winners of the better leagues and 3 POTS depend of UEFA coeficient of teams.

I'm sure that can be difficult to create something like a coeficient of CL and for example, and do a ranking of the teams based in CL history to do the groups so, my suggestion is that every group have to have a League winner, a 2nd, a 3rd and a 4th.

That simple. I think is really a fair rule, guarantee variety no?