One low-cost way for you to experiment with this concept to see if it works, and to then help you decide if you should invest more money in the way you described to give each nation its own special HBG unit, would be to:
Pick up a copy of A&A 1941
Extract from it the unique sculpts that represent weapons which were actually used by the nations which produced them, and ignore the ones which are “national mismatches” (American IS-2 tanks, and so forth)
Designate them as special units and create (or find) house rules to govern them
To give some examples:
The tank sculpts in 1941 represent German Tiger and Russian IS-2 tanks, both of which were heavy tanks. Those two nations would therefore have the ability to build heavy tank units.
The battleship sculpts in 1941 represent the British Hood class and the Japanese Kongo class, bot of which were battlecruisers. Those two nations would therefore have the ability to build battlecruisers.
The other units aren’t as clear-cut as examples, but you could use a similar technique. The American Sumner-class destroyer could be used to represent destroyer escorts (which, I admit, they weren’t). The British Lancaster could be used to represent a bomber with a super-heavy lift capacity, the Lanc being the only Allied bomber which was long enough and powerful enough to carry the Grand Slam super-heavy bomb. And so forth. The point is that one single copy of this game, which is fairly inexpensive, would give you lots of unit types with which to test your concept.
Interestingly enough, I actually had a new 1941 at one time (I got it as a Christmas Present), but returned it for the very reason that each nation didn’t have unique sculpts. I grabbed the Seafarers expansion for Catan instead.
But thanks for the idea.