Making on the total CS (including militia) would alleviate the potential to get it in one shot. And as long as the cap isn't ridiculously low, people would need continuous battles to maintain it. The tweaking would all be around how important the effect is desired to be, I see a wide array of possibilities into what the numbers could be before dipping into the excesses.
However, I will agree on your second point: changes do take a while. Is this more important than other codes on the to-do list? I'm not inclined to think so, because I don't really see the need for it. I kind of see it as a reversed and watered-down version of my earlier variants to "too much peace" (back when that still plagued us, my suggestion was that it should not affect region control in any way, just military capacity such as troop morale and recruitment rates, therefore rewarding realms that take risks and go to war, and weaken realms that try to play it "safe" by avoiding all conflict). This feature request, the way I see it, adds a wee bit of realism, and an overall increase in military capacity to all those fighting. Pretty close to a zero-sum bonus, strategically-speaking, even if it is tweaked to favor some fighting styles/conditions (ex: to make dying realms harder or easier to defeat).
I just don't buy that it's a balance issue.
