This is kinda fun.

Since you mention it, KarmaInferno, *mil-spec* is already something for the military and not runners.

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The SC2 armor is right between armor and vehicles, because it's your basic 'manual power armor'. In SR4 rules, if it existed, I think it would be clearly a vehicle, albeit one that requires a metahuman pilot. Piloting it might be a Pilot Exotic (on the grounds that it's an exotic item, and you 'drive' it with mostly normal movements), but the point of feedback-style power armor (Starship Troopers?) is that it basically moves with you. In order to handle all the extra features, I'd go ahead and require a Pilot Exotic.
As for stats, you'd have to start from the ground up. It's not a Tomino, but it's not mil-spec. Balancing a wholly new item is icky, but it could be fun in your game. The fact that it doesn't exist in the setting means it's a late-stage prototype or something, I guess?
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MJOLNIR armor looks lighter and thinner than the SC2 stuff, but I think that's just a trick of the proportions. It's actually 1000lb of DNI-controlled (always Jumped-In) exoskeleton (vehicle?) with a piggybacking AI (Agents, I think, for SR4), and you have to have skeletal augmentation to use it (I'd also say maybe a datajack is required, but technically trodes in the helmet would be fine). It doubles lifting capacity and multiples reaction time times 5 (I think the Jumped-In bonus is good enough here).
The armor has gelpacks, autoinjectors, and a power supply. The helmet has all the normal mil-spec upgrades. Magnet strips on the back to hold weapons. Shields (no way to put this in SR4). Etc.

It might be *simpler* to treat MJOLNIR as normal mil-spec, but it'd be nice to keep the DNI/skeleton requirements.

That's what I'd do, anyway.
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So, would either of those work? If they're vehicles, they don't take stun, but you could require Hot-Sim (dumpshock); also, the 'passenger' could still take damage from major attacks. Attackers can technically just target the 'driver' directly. Hmm. If they're armor (esp. MJOLNIR), then you don't have that issue.