I also think that proto-Foehn should have some special stolen tech and other in their Origin campaign, which would work as a sort of precursor tech for them. Like how they got to build early Future Tanks in Tainted Empire, or maybe getting the Infector Tank too later. Maybe with Rashidi's help, they could get the Syckle. The Iron Dragon is obvious. Maybe the Grumble could be a potential connection to the Golden Rocket tech, for example. And later in Act 3, there could be a mission all about finding the last intact Allied Tech Center to find the mirage tech and develop the Phantasm.
And maybe in Act 3, since the Epsilon (or Reptoir) controlling most of the world, they could have access to "hybrid" tech, as in, other stolen tech units, like all the Epsilon ones (with modified Salamanders that don't use Foehn tech, and such). And of course, just like with the Cyborg Prototypes, the campaign could use other cut units as well.
Campaign is all about interesting scenarios and battles that would be unlikely in MP or Skirmish, so a "regular balance" doesn't really make sense, so the MM can go wild with the different sort of units and whatnot.
(Also, I'd still love to see a tower defense mission, with all sorts of custom towers.)