In my opinion, the crucial point is to figure out what makes aiming an equal contestant to a) the additional attack granted by choosing 'battle' instead of 'ready', and/or b) the interrupt attack granted by the guard order. Those two alternatives give the hero (another) full attack, so if aiming want's to find its niche it has to be as powerful (and relevant) as battling and the guard order. Considering that, I really like your "Option 2b" and believe under such rules, aiming could play a roll against monsters with higher armor (like or especially boss monsters), against which an additional attack has the drawback that is has to overcome the armor twice. On the other hand especially THAT aspect of an additional attack makes monsters with high armor strong - if you reduce the advantage of armor over wounds, it merely becomes additional wounds. Still, I'd like to give it a try and will so in my next game of descent - which, unfortunately, is not yet on the horizon. Perhaps you playtest your suggestions yourself and report your findings? I'd be interested in how they affect the game.