I promise this will be my only post on the subject. I mostly lurk anyways.
I share the trepidation regarding one unit per tile. Artillery shooting over tiles I have no problem with (although not sure about archers..)
It strikes me that there are a myriad of more obvious solutions to the stack of doom problem.
Flanking is the really blindingly obvious one.
The one I quite like the idea of I will describe below. It's not polished, it's just an idea, but I quite like it. That way no one can accuse me of just moaning
The situation reminds me of Dragon Age. Complete speculation, but when you have long running companies, people grow old, people move on, new people come in. Dragon Age, with it's click-to-do-more-damage mechanics, probably seemed like a great idea to someone who grew up with Diablo and World of Warcraft. It was anaethma to me, who grew up with P&P rpgs. These changes seem like a similar thing. It happens. I don't like it, but it happens.
Anyway, the solution I would have liked to see is to allow stacks of doom, but restrict the numbers of units that can actually fight. That's how historically small armies beat large armies; by fighting only a bit of them at a time. That's how Napoleon almost won Waterloo. Also, I'd make it so units didn't die so easily, they could take much more punishment, and at the end of combat you'd have damaged units but they wouldn't die; but you would take the tile. Defender would get choice of unit to fight when it came to damage, but attacker would get choice of unit when it came to taking the tile. And if you take the tile, and there's a whole bunch of other units that didn't fight, they take a sort of collatoral damage through being forced to retreat. Or maybe not, I dunno, it's not my job to figure out the details
But really, there's all sorts of clever things you could do with combat. It seems a really strange choice to restrict it to one unit per tile. I wonder what there rationale was? I wonder did they consider any alternatives? I also feel a sort of told you so. I don't like the suicide catapults in Civ 4. It was lame. Sure, it did the job of providing a way to deal with stacks, but there are so many better ways. At the time, it seemed like everyone was saying it would be great. Does anyone still think that it was a good solution? I think it was a lazy solution. This seems lazy too. People keep saying "But it's Sid Meier! It'll be fine!". Half of me thinks "Yeah! Pirates! Covert Action! Civilisation!" Half of me thinks "Suicide catapults & pointless fortress improvements".
I'll wait and see and maybe I'll be surprised. Otherwise, I'm sure Paradox will be coming out with EU4 sometime.