I'm not really sure about this suggestion, I would like to know what you think about it.
It's not fair at all that you might lose because your opponent had a hidden core. Some years ago you knew someone could forces you because you could see the azrael gun. Now this core can be in any gun you want. You won't expect to be forced when your opponent has another gun, but yes, he/she might have forces in his gun. And I know it because I have bought forces for some of my guns. Tired of always using azrael gun due to forces I decided to buy it for other guns. And every time I forces someone they just are surprised about that move, and sure, if they didn't know I could do that.
In other cases it doesn't matter if your opponent has a hidden core. The other case that always happens is piston punch instead of generator. That has a bit of estrategy, and showing up the cores you have might ruin piston. However azrael will being hidden is the worst thing could happen.
Maybe you could just add next to passive a image of azraels will. In this way cores keeps hidden except forces.