Glad to see another Ringo fan. I have a few ideas 'bout infantry too if you don't mind. First of all, as much as i'd like to see un-armoured infantry in this game, i think they'll be a bit silly. Considering the extremely varied conditions in which the fighting occurs i doubt a human could survive outside of a sealed enviroment (kinda hard to breath if the atmospheric density is 2.3).
So going off the armoured idea, just how mobile are the infantry? Jump jets and bouncing is entirely up to the design team but i think it would be really cool if the infantry didn't have a radar signal unless they bounced.
Either way the next question is about armament of the infantry. Considering the large amount of armour on the battlefield the infantry have to be able to care for themselves. As much as i'd love for them to be the king of the battlefield, thier weapons have to be in proportion to the weapons that currently exist, so i'm thinking mostly unguided rockets (cheap but effective, probably low ammo count too).
As for the deployable PDW i would stay away from them, infantry's (especially mobile infantry if they are implemented) greatest assest is manuverability so please don't tie them don't to need fixed positions. Also i don't think the grunts want to carry more gear than they need. I would recommend having an engineer squad that could drop the standard turrets and capture buildings, but please don't give deployables to the regular troops.
Just throwing some ideas around, feel free to ignore me (most people do). And to address the issue of cost, modern soldiers are expensive to train and equip. But no matter how cheap the soldiers are in comparison to the tanks, humans are always more expensive in terms of time.