Well, I did intend original six player nations to be: France, Germany, Poland, Hungary, England and Italy. The two already defined spare positions were: Aragon and Scotland. Scotland is somewhat poor in income, but has the wealth of many dukedoms compared to it's size and it would give more action to the Isles.
Burgundy on the other hand has only few dukedoms and being in the middle of three most powerful kingdoms (Germany, France and Italy), it is not a position I would suggest taking...
Also viable positions are:
- Sweden (biggest Scandinavian kingdom, quite large in land area actually)
- Naples (close to moslems and is decent in size)
- Castile (several rich provinces and an AI kingdom of same culture next door)
EDIT: I'll sum up the rule collection in the first one or two posts.