I will work on both. The Cossacks units are almost "finished" as far as I'm concerned. Making the remaining ones requires a lot of copy & paste, and I don't want to make it anymore.
I will do some, the one I really need in my mod, but then if someone want one of the remaining unit, then he has to do the copy & paste himself, and then I'll finish the unit.
If nobody does it, I will eventually do it myself, but it will be very slow, as I have a lot of other projects going.
On the other hand, I can code a special version of SBB that can procude very fast a full storyboard for an American Conquest unit. This means production time divided by 10!
So I will work mainly on American Conquest once I have finished the Cossacks units I have in stock (5 of them). Of course, I will also complete the units Loulong is working on.