Boomer
There are a select number of leagues that are considered the top leagues in the game, for example (there might be more in this list):
2 car 50% distance has International GP Championship, The MJL, and International F1 league
2 car 100% distance has The F1 World Championship, British Racing League, and European Racing League
1 car 50% distance has iGP Champions
You'll find most the the top managers in the HoF to be in some of these "top leagues". It's not just their rep points that make them the best either. Unfortunately due to constraints of time zones, they may not be convenient to players from certain parts of the world.
Still, I think before thinking of an "iGP Super League", the league search function must be greatly improved first, so you can better filter leagues based on average reputation, activity, and so on, similar to what I mentioned on another thread about the league search function.
Now I have been keeping an eye on this because I really want to join such a league, however I found I had to keep on searching the HoF to see in which leagues these drivers are.
I think it would be rather simple, the "Spectate" function has an average reputation for the managers of a specific league. So how about adding a tab in the HoF for leagues based on Reputation. Then you can clearly see the top leagues and see where your current league stands, I think this will push active players either into more active leagues or have leagues be more focused on activity.
If you then want you can add a Reward system for the league leader board if you really want to, but in effect the top league would count as an IGP Championship league basically.