personally i would remove the distinction between stackables and nons, just having it be permanents in general, and have it only be triggered when your opponent destroys them (as in a binary event, were one or more permanents removed by an action? if yes, draw 1 card), the lone exception being bonewall for balancing reasons
something along the lines of "draw a card when your opponent removes your permanents from play" or your field or however you want to balance it.
i like the mechanic, i just have a hard time supporting potent cards going to the fire element lol