Allowing for personal taste, degrees of detail and varying emphasis on command or morale and such, when it comes to transitioning from 5 to 6 man skirmishes to 50 or 60 in an all out brawl, the only real difference I see is a 'unit' shifts from an individual model - with particular stats and abilities - to a group of models with the same, just more fire power and wounds. The trick for mass combat games seems to be how to handle large quantities of miniatures smoothly and efficiently.
I'm not sure you can scale rules for individuals up to squads/platoon level without serious abstraction and simplification. I mean, you're not gaming with hundreds of individuals, each with their own unique stats. You have simply grouped 50 or 60 miniatures into 5 or 6 or 7 units. In the end, aren't you just back at the skirmish level - but with loads more dice and models?