Johan:
When we started with making content for EU5, we went with 3 categories in how much focus should be spent on them.

Tier 1 for the major great powers who impact the timeline the most.

France
England
Ottomans
Castile / Spain
Muscovy /Russia
Austria
Yuán / China

Tier 2 for important ones and those that you all love playing

Byzantium
Venice
Brandenburg / Prussia
Portugal
Sweden
Denmark
Poland
Mamluks
Japan
Delhi
Holland / Netherlands
Timurids / Mughals

Tier 3 for everbody else we wanted to make content for, everything from Mali to Scotland goes here.