I think the exo-suit idea is brilliant. By itself, it's the equivalent of a forklift or similar small construction/utility vehicle, but optional armor and weapons could be included on the basic frame to turn it into power-armor.
It doesn't really need a separate figure to be faction-agnostic - in fact, it's probably more useful with an integral, generic figure, which doesn't look much like any particular Death Fields army (a generic jump-suit like the black outfit the guy in the first exo-suit picture is wearing, or generic light armor of some indeterminate sort, with three or four different pilot heads in goggles, industrial masks, mining hats, or whatever, would be fine.) Otherwise, a lot of modeling or an unnecessarily complicated kit would be needed to fit whatever poses your given figure would be in, where a generic figure would be in exactly the one pose needed to make sense. As long as the head is separate to allow head-swaps, I think that alone would be plenty to clearly identify which faction the pilot is part of: the various Death Fields factions have some fairly distinctive gas-mask heads that, combined with th generic body painted up in team colours, would surely do plenty to give the pilot a uniform look that would fit the rest of whatever faction it's assigned to.
I think the exo-suit models would get the most bang-per-buck with plenty of modular custom options for different cockpit designs, different hands, different styles of armor, and the like, so that two gamers could easily each build a set of exo-suits for their respective armies, and have them look different enough on the table to have been made for different teams/armies.
Options for claws for lifting heavy loads, saws and other tools of different sorts, communication gear, and various heavy weapons on standard mounts, too, to weaponize it further: standard mounting "hardware" would allow these bolt-on weapons to be swapped to other vehicles, too: the bolt-on flame thrower or rail gun might be mounted instead on a motorcycle or light truck or tripod or other hypothetical vehicle, for example, or weapons from future model kits might be mounted on the exo-suit using the same connection. (I haven't seen the Grognard set yet, but based on the review I saw the other day, I think those weapons mounted on their tripods and carriages with this sort of standard connection - that same standard connection point would be pefect!)
Even as-is, though, I can imagine the scratch-built customizations would provide a lot of variety: polystyrene rods and card to scratch-build armor, for example, or spare missiles from scale model helicopters and jets to glue to the exo-suit arms....
Whatever the case, a good exo-suit/power-armor kit with, say, parts for two suits with an assortment of armor and weapon options could probably be done as its own boxed set, and would surely sell well: all sorts of sci-fi games can make use of the basic power-armor and even exo-suit idea, especially one that allows enough customization to fit the model into the game or faction's style.
And, all that reminds me: I really really hope Wargames Atlantic and the folks behind Iron-Core bring back that Eisenkern Stormtrooper Accessory set, with its great robot-mule models (but hopefully with simplified legs - the mules' legs make the WA giant spider legs seem easy to assemble!). I think the Raumjager and Eisenkern stuff suggest a similar enough aesthetic that accessories for one woud work great with the other:
