Currently all talents in the game are a straight upgrade, with the possible exception of assassin. I feel it would be interesting to have talents that were a mix of plus and minus stats. These would make weapons have more unique feels, rather than being straight upgrades. A few hypothetical examples could be below.
Hollow points: +X% Headshot damage -X% Damage
Custom Interior: +X% Firerate +X% Recoil/Stability
Bladed rounds: +X% damage -X% Range
Heavy duty: -X% Recoil +X% weight
Spring-loaded magazine: +X%fire rate -X% mag size
Bare Bones: -X% Weight +X% recoil
Naturally, these talents would be biased towards the positive stat, with higher on average stats than the non-negative talents. They wouldn't be better in every case, just on average.