Maybe for generals and captains. I'd like to see them defect to the other side without losing their units or changing uniforms. Generals kinda have that in the trait system. Captains are more bribable. But to have them desert for more than a gold coin would be nice. Maybe the farther and longer they fight away from the capital, the higher the chance they could go over to the other side. If your treasury gets too low or squalor or corruption is too high, they'll say enough is enough. To fix this maybe you'd be forced to place a taskmaster pro-consul to influence your far-off garrisons.