Just give a good reason why there should be a limit on numbers of troops per tile. I can't think of any. I think it would suck immensely. I think it would be a sort of thing that would bug me when I'm playing, and thus diminish the enjoyment.
Ok, possibly this might somehow be used to enhance game play. Like something you mention in the end of your post. But it damn well better enhance it then, because if it'll just be that, a limit on the number, and nothing else, it'll just be a nuisance. That's my prediction anyway.
I do however wonder how a civic could realistically add to the number of troops you can have in one place. The Make-slimmer-troops-by-eating-more-veggies civic?
And the general, what would he do? "Huddle closer together now, boys. Don't be shy." The gay general. :P