Well, I can picture as a GM, and the use case is practically the same. Essentially, no rune tracking is the big one. I'd want a movement to be free/untracked so the mob can move around as needed. I'd want damage to be fixed, and maybe all at the same time, so they are in effect amplifies on each other (one swarm member next to you does X, two does 2X, only one defend in either case, say)
I think it really comes out to that if I have to have a play mat for every swarm member, it's going to suck. If I have a play mat for the swarm itself it's probably fine, but still a bit cumbersome. I like the one hit drops idea, but I think your example of 3 points and they go down is very close to the same. It means that area and multi really gets the strength on these (hit 3 for 4 points with an area bone snapper, you take out 4, as you just did 12 to the swarm)
In my mind, a "swarm play mat" if you will is probably much smaller... Top part of the mat mostly, with almost no conditions. They might not even really be able to do contingencies. In hand, in play, in essence, or death/drain and that's it.
Also, I might say that mental damage just becomes physical damage. If heal can abstract reinforcements, mental damage can abstract running away

edit: some more thoughts on swarms (which I might accidentally call mooks on occasion)
--- on the model I think about with them---
In Feng Shui, mooks are one hit and done. You increase your difficulty to hit more than one, or you have a power that allows it. I like this model for it's simplicity
In 13th age, mooks are directly derived from Feng Shui have 1/5 the HP of a normal creature. They also have overflow damage. That is to say, if you hit a 5 HP mook for 10HP, that'll take out another mook. The player or the GM is to make up a reason why it got the other mook, even if it was across the map. If you hit an area of them, that amplifies the damage (whole mass takes number of members hit * full damage, which tends to make fireballs rock on them). I like this model for it's ability to handle the high damage numbers.
My gut says that the 13th age model is a closer match to FotN. It means that Egil can Amplify power attack and do a truly stupid amount of damage, cutting off a mooks head and knocking someone out with the head as it hits the other guy between the shoulder blades. it means that Freydis can area up her bonesnap and take out a truly staggering number. I like this because it makes the image of the coming Ragnarok pretty epic - think Viking Dynasty Warriors.
I think your "3 hp, remove a model" is very close to this as well. It's the damage of a weapon roughly (weapons are a little light for this particular example), and that matches about what 13th age did (mook HP = avg damage for a weapon on a hit)
I also found in 13th age that it was hard to manage more than two groups of mooks at a time. You had to keep track of the groups separately, and a lot of movement.
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Another way to think about swarms - what's the difference between a swarm and a moving alka? Imagine you summon an alka with the (As yet created) "movable" meta. It can move some number of spaces per token. It still has to be contiguous (or close, with Stutter). It's effect is "do X DF to an adjacent opponent". If you don't maintain it, it drops after getting "hit" once. I think the primary difference here would be that running through the alka space wouldn't bestow an effect, it would end it.