If you mix nations, you can't call that the Napoleonic Wars World Cup. And as Golden said for Ireland, some teams don't have enough players to make a proper tournament. The only way I see if you want to organize the real NWWC is the 5v5 format.
Mixing nations is a good idea if you organize a new tournament which is similar to NWWC. It could be the last big tournament of NW. In France, we could make two teams, we could for example mix Sweden/Finland/Norway, Austria/Swiss, Spain/Portugal etc... We should allow nations to mix with others nations, then they can make as many teams as they want. With that we should be able to have enough teams to play an enjoyable tournament like in the past.
This would need experienced organizers.
I repeat, to me a NWWC would just be FRA VS ENG, there's no points of doing that.
What do you guys think of this idea?