I'm thinking about Historical games using the WK system, as I'm not a great fan of the fictional setting.
As my main interest is in English history, this is my preferred field; there were about 40 counties in Medieval England so they should work as a basis for territories, possibly accommodating 7 or even 8 players.
Two scenarios are obvious:
"Magna Carta"; King John and the Barons
"Wars of the Roses". This might tend to morph into a Warrior Knights/Kingmaker crossover, but then WK was clearly inspired by KM...
What would be different is that the player would control a Royal Heir in place of the WK "barons", with his subordinate nobles doing his bidding rather than the other way around as in KM.
At the heart of the system would be my inheritance rules with much more happening when a noble dies. Also the emphasis would be more on killing off rival nobles and heirs than on capturing cities.