I had this idea for a while now. Now that reserach biomass shop is a thing, this can actually work.
The biggest problem Greenos currently have, is that they dont feel really like something that fits into the USMC. Its a giant bug, nothing to make it look like its property of the USMC. Nothing that makes it look like it is figthing for the USMC. And also, you sure as shit know that a general that would make such bugs, would modify the hell out of them to make em stronger.
So, how about reserach can buy with biomass, armor for xenos. One for each cast. This would, of course, include an armor buff. But also for some casts uniqe additions. Maybe a seat so people can ride runners like cavelery into battle (you know you want to see that). Maybe Allow you to install a M56D on a charger. (that one is dumb and way to OP, but admit it would be badass as fuck.)
Honestly, i cant think of many uniqe things that wouldnt be broken OP.
but still. Besides the saddle, thats just needed. Giving them an armor buff with those VERY EXPENSIVE upgrades (about as much as the xeno would give +200) would still be a cool thing to spends points on to invest into greenos, and it would give them cool armor drip.