Enticing propsects in every sense. My vote and reasons go as follows:
1: Russian 1812 infantry in MAC format.
Reason: You do not have 1812 Russian infantry in your current range, there are relatively few choices from other makers; and you could sell lots and lots of these figures! I would certainly buy them.
Similar to rationale for the above, excepting that your existing Napoleonic Austrians have served well but could do with replacement - sorry, but there it is...and I do already have 8 sets of your Napoleonic Austrians, so I have done my bit for them!
3: Prussian Landwehr MAC
The Airfix/ HaT 1815 set seems not to be readily available, and although it has some charming figures it is a bit dated and difficult to form units from ie: based on the poses included. Clear need therefore for some good MAC sets - I envisage large columns of rugged 1/72 Prussian Landwehr marching to the sound of the guns!
4: French marching
Someone has yet to design and market the definitive French 812-15 marching infantry set. And let's be honest, the market for these could be huge. How many figures would one need to provide a convincing D'Erlons Dividional column in march attack on the table top? Hundreds is the answer.....Sound the 'Pas de Charge'..
However, there are lots of French infantry already around....so they come in 4th on my vote
Many thanks, hope to see them all in production in the next year or so.