The same discussion was going on on twcenter forums :)
In my opinion, while it would be foolish not to include the united provinces as one of the 50 factions, i think it shouldnt be one of the 10 playable.
They werent a continental power, they were really dependant on GB for their survival in europe (military speaking).
Look at the 6 named factions, look for 4 factions to be included, i dont think the united provinces could come on top of these.
Russia and Austria should be on the top priority to be one of the 10 playable factions, even if like prussia they were not naval powers, but truely had an empire at that time.
I hope we'll see 2 "exotic" factions as the last spots :)