I'd like to see a line of nanos added to soldier that enhance the clip size of a gun for certain types of ammunition.
Another idea could be either a line of nanos, or a tradeskill, to "enhance" the power of the ammunition that is used (in the form of increased attack rating). For example, "enhanced" energy weapon ammunition, "anti-matter" energy weapon ammunition, "kevlar tipped" bullets (with bonus against kevlar armor) etc.
Of course, soldier only.