Re: No peacetime, no militia rush!
And the Heroes series are another story, that's like nothing related to KaM, except for the fact that it is also an RTS game.

But you're right you can't compare KaM to Heroes 3, because in heroes 3 everyone has starting troops, and you can't exactly "rush" the enemy, because he usually puts soldiers in defence, and it's harder to siege than to defend.
(look, a game where it's harder to siege than do defend, I wonder why nobody complained about that back in the days of HoM&M 3, because currently people want to attack and win

In Starcraft 2, everything is built very fast, so you can quite easily fight a rush back if you have a unit-creating building.
In SC2, you need only two resources for everything, mineral and gas which are directly added to a global pool. It's totally different from KaM where you have to do the unit equipements, do a recruit, and wait for a serf to bring all of that together. It's slow, and I don't think we can invent solutions directly from that game, because they aren't supposed to work the same way.
I'll try to think of a solution from a more slow-paced game that I played :
Anno 1404 : (multiplayer games are even longer in anno 1404 thank in KaM, and I played quite a lot, so here are my observations).
.in this game, everything is slow, quite like in KaM, except the creation of buildings which is done instantly
.in this game everything needs different resources, like in KaM, and these resources need to be brought up to storehouses (which have a global pool per island) via roads, like in KaM. In this game, it's long before you get any troops, like in KaM.
.in this game, there are woodcutters, stonemines, gold mines etc, and although there are differences in the use of these resources, I think we can certainly do a link between these two gameplays.
.in this game, citizens eat, like in KaM, and you lose population if you don't feed people correctly
.in this game, when an enemy destroys your economy, you have a hard time rebuilding it, like in KaM
I'm done here for the arguments showing that Anno 1404 is a good test subject to think of KaM gameplay.
The warfare in anno 1404 is quite oriented on naval battles obviously, but let's take the example of land battles :
if a huge army comes on your island, there is an area around each army settlement which prevents you from building, but outside this area, you can still build instantly. So if you have the resources needed, you can build towers arund the enemy, and here starts the siege part of the game, the enemy destroys your tower and tries to make his safe zone (preventing you from buiding) bigger. Meanwhile, the defender tries to get more army recruited to have a chance to win.
So, like in KaM, if a bigger army attacks, you enter "siege mode", and like in KaM, you can't build towers near an enemy troop otherwise it gets killed. But if you see an enemy starting to siege your towers, you can build more behind, and we cancertainly think of an analogy between those two gameplays, because in KaM the attacker tries to extand his control zone on your city, while you try to buy time to get more troops.
So I said many things that are "like in KaM", there is only one thing that isn't like KaM. And it's a fastly built defence building.
So imagine a "rush" in anno 1404 (yes rush is quite slow in this game, but you can still rush.), the enemy is on your island, you don't have troops yet, what to do ? You build towers, try to buy time, and then you have a chance to survive.
The main point being :
in KaM, ANY way of recruiting troops is too slow if an enemy is inside your city an you don't have towers. Being able to build a low-resistant simili-tower with serfs bringing resources directly to it without the need of a road and quite fast to build seems like an idea to try, because if you can slow the enemy, you have much more chance to recruit enough troops.
It should not cost much but still if you spam it you'll slow your economy so you'll have to place them well.
The problems being :
-a new building, sprites, people not being used to build it
-transposing an idea to mimic the gameplay of another game might be a bad idea
-I surely have flaws in my reasoning
-I like anno 1404 too much
-I didn't take naval battles into account, because in Anno 1404 if you destroy a trade boat on an important road, you can kind of starve the enemy and do huge damages to his economy
-MIGHT not be that useful on all the maps, depending on openness
-in this game it's quite hard to siege too, harder than to defend anyway. (no link but I wanted to point out, who knows why)
Sorry for the reading.