I'd like to see development focused on factions which played greatest roles during Napoleonic Wars. Imo there should be Austria instead of Prussia, but let it be after because of already started progress of Prussia. Then Russian Empire, we cannot forget about first power which stood against the Emperor. Then all those weaker or less important in NW factions should appear in any order: Italy, Spain, Duchy of Warsaw, Rhine Confederation, Ottoman Empire, Scandinavian states et cetera.
It's a lot of work and it's hard to believe that devs will have time and money to complete every single faction i'd like to see. That's why i'd be grateful to see modding tools released in short time, or at least map editor and opportunity to make uniforms simply. I'm pretty sure that in community such filled with reenactors, will be few skilled enough to make additional factions even for free, as long as this game is focused on niche community. That's probably easiest way to complete this game without additional cost, in shorter time and to avoid it's natural death before official release.