This is a concept I've had in mind as well! Some approaches to it that I've seen so far include:
* Discussion of "tiers" in Vincent and John Harper's Knife and Candle hack (will probably have to wait for it to be published to see what comes of that, and using it in your own hacks might be less permissive since it will be a licensed game). In this approach, at least in what's been discussed publicly upping a stat to +4 resets it to +1, but you're in a new tier. When acting against people on the same tier, no problem, it's the same. Acting against people or things on a lower tier, you either just succeed flat out, or else anything on a 10+ counts as a 12+ or some other "wow, great success!" way of doing it. When acting against a higher tier, you need a 10+ for a usual 7-9 result and a 12+ for a normal full success
* John Harper's Eye of Chaos has a peripheral move where you get +1 when contending with something beneath you, -1 for out of your league, and -2 for beyond the pale. This might be where the 'tiered' thing ended up going since he's admitted that Eye of Chaos has some 'test' stuff for Knife and Candle
* In "Beneath a More Auspicious Star" (basically a Romance of the Three Kingdoms hack) Stuart Chaplin talks about personal scale and strategic scale moves. I think his going idea is that some moves work on both scales, but have different effects depending on the scope of your conflict. This is meant to capture the whole 'one guy leveling armies' thing from RoT3K
* My own hack, "A Song of Ice and Fire" (yay plugs!) takes the approach you suggest of going totally loco with the gang scaling and adding some special caveats, like a group of men on horseback fighting a group of men on foot counting as one size bigger. Basically you have multiple tiers of "small, medium, large". On the personal scale it goes from a few guys, to 10-12 guys to 15-20 guys, say, then on the unit scale it goes from 20-30 guys to 40-50 guys to 60-70 guys, and then on the army scale, et cetera et cetera. When a group from a larger bracket acts against a smaller tier group (like an army-scale group against a unit scale or personal scale group, for example) they just win. I haven't tweaked or playtested this yet, and it's meant to be more gritty than epic, so it probably won't suit your needs
So, that's all that I can think of off the top of my head for scale stuff, but if you poke around a little (especially in the hack forums and blood and guts) you'll probably find some other interesting stuff.