I was thinking about this a little more.
We could also add arbitrary rules if we make it Risk-like for things like movement in the map. Lower-rated players would have higher mobility (like infantry) while higher-rated players would move slower (like heavy artillery).
Excellant idea and excellent further thought too. Making the very stong players slower moving like artillary is pure genius
I've never really played Risk, but this sounds good.
I like the idea of this being a clan based feature, I think it will be more fun and will make it accessible to players of all rating ranges.
As I understand it, Risk involves battles with a die? This could also be incorporated into these Risk-like clan challenges. Before the battle commences certain games can be weighted (randomly) or count more than others.