Sounds intriguing. I'll admit to being pretty unfamiliar with the capping dynamic as I really haven't played many maps which work that way, like with a hard limit beyond the purchasing phase. I gather the idea is just to reduce the size of the forces in play overall? I'd guess a stack limit would basically force attrition over time, or to prompt players to spread forces across multiple tiles, whereas typical A&A gameplay favors the consolidated massive stacks in just a few spots. I feel like AA50s approach to China was like that (though restricted to just a couple unit types owing to the nature of that faction in AA50), but I just mean that limit on placement at 3 inf per tile. I wasn't a huge fan, cause it made it so easy for Japan to steamroll them lol.
I think production values and unit costs or first strike/aagun type mechanics can be used to mitigate some of that stuff, but clearly not all of it. Even with artillery, and maintenance or build limits on certain unit types, the fundamentals still kinda lean towards deep stackfast probably, just by the nature of the beast lol. I know it's a perennial concern for big maps with big stacks, though I suppose I don't mind so much if everything else is humming. It's hard for me to visualize, but I can see what you mean if it adds a lot of tedium with the click click or makes it so that it's hard to parse what sort of forces that the opponent can muster for a given fight.
Not sure what approach is best. Guess it kinda depends how the limitation is framed for the conceptual buy-in. Like with Aircraft you could probably rationalize it based on airfields allowing for a certain capacity per tile, sort of like a fixed aircraft carrier but which can accommodate more air units than a carrier does. Doing it like that it'd be more of a soft build cap I guess, like where the ceiling could be raised if the player purchases more infrastructure maybe? Like using the bases as the limit there, but allowing them to be improved over time for the associated unit types. I think as long as it doesn't devolve to a slogfest with the player incentivized to overproduce ground hitpoints, but where they don't have a way to make breakthroughs without enough heavy hitters to crack the fodder walls hehe. Of the standard boards, the familiar prob from Classic boards or like v6 without artillery, where the play-pace is super slow.