I was thinking, instead of just adding penalties to envirosuits and armor (afterall they are there to negate those same penalties from rad poisoning and stuff.) just add engine and weight to the equation? like with vehicles? there would be a choice for weapon, envirohazard, armor and "engine".
enviro choices would be the around the same as the choices from turn 1, from filters to envirosuits, and later mark II, III... to make up for the increase in enviroprotection from the armors you currently research. it would increase weight and cost mainly IP.
armor would go from basic armor (the 50 armor protection the envirosuit already offers), "padded armor", combat armor, etc. it would increase weight and cost mainly metals.
engine would start at servomotors, then advanced servomotors, these would cost no fuel or energy as they would be "negligible", then "jetpacks" (which could be renamed propulsion engine, to imply they don't necessarily fly) which would cost fuel or energy (by then you would have ways of generating infinite fuel and energy from deep core mining and stuff.), "advanced propulsion engine" and so forwards.
basically by default if you put the heaviest stuff , best engine and engine design 100 it would offer a small penalty in move speed but negligible or no penalty in combat. if your engine design is worse the penalties start getting noticeable and if they are better they negate, and if your put light armor and overpowered engine they start offering bonuses in move speed and combat eventually becoming + 40% move modifier and the same combat bonuses as the current jetpack with the propulsion engine and light armor.
the problem would be redesigning the "jetpack infantry", anti-tank and artillery, which already have big weight modifiers from they're guns. but if they use lighter armor that wouldn't be a problem i guess.