I've just an idea, and I'm quiet sure nobody talked about it.
My idea is to add, a custom skin for the units, different from the basic one, to represent the NCO's on the field. The player could select between a variety of NCO's. I was thinking about stripes, to distinguish them from the basic soldiers.
Actually, I'm speaking for the French, because I don't really know how the different ranks were managed in the British army.
For exemple, a picture that shows the different NCO ranks in the French army during the 1st Empire:EDIT:
This was proposed by Caselius. He talks especially about the British ranks.
I've always wished for proper NCO class.
And what could also be interesting that they would get the ability to have the Spontoon for some nations in addition to the musket or ability to choose it separately from the class selection.
British rank system was pretty similar to the used nowadays, chevrons displaying the rank. Regiments however had their own styles on the type of the badge but ranks themselves were standard.