I like it. Rather than linking it to Nuclear just call it Paratroop cards or something similar (airdrop, whatever u fancy) as this is what you're doing in effect, by wiping out the enemy in a surprise attack wherever they are and then replacing their forces with your own.
As a varation u could build on the existing colour schemes
RRR gives u 1 army per region (or 4)
GGG gives 2 per region (or 6)
BBB gives 3 per region (or
RGB gives 4 per region (or 10)
As for the comment about being unbalanced on smaller maps, well, either limit it in some way (50 regions minimum) or put up with it - it's the same for everyone! Being lucky a few times will get balanced out in the long run by the opponent getting the draw first on others.