the answer to that is "yes"

it is scalable to fit your system requirements.   Chances are that  20,000 will be rare,  unless they make some dramatic changes troop production times and training interface.  But I'd wager the goal is around there in terms  of being able to support troops.  So if you have 2 particularly lethal stacks in a 30+ hour game, perhaps numbers could climb that high.  easily with some modding.  thousands for sure, if not 10s of thousands. 

the further in you zoom the more individuals can be seen.

Didn't you know? It's a well known fact that all game developers get a permanent +5 Bonus to their "befuddlement", "confusion", and "illusion" skills for the duration of their careers. They are also born with those skills and if they need to train them it only cost them half the experience points necessary.....lol.

I think that, while on the world map an army is represented by a single Icon (preferably the general, or a dragon if present), the battlemap will be scaled to the relative troop sizes. Therefore, a small street-fight between 50 soldiers and 20 trolls will be a much smaller map than an Epic Grandiose battlefield, with 10,000s of soldiers, and each unit of the battlefield maneuvering precisely and elegantly, like notes of a concierto... Or one side could simply zerg rush the other side, being completely unorganized and gaining a marginal charge bonus. (cavalry would have nice charge bonuses, of course, although organization would still be preferred)

I assume the leadership skill of a General (and/or Sovereign) would determine the ability of his troops AI to act in a manner befitting the enemy. (also perhaps you could assign units(or entire wings/divisions) "battleplans" like in KOTOR, Mass Effect, or Dragon Age)

pausing for every turn would only be necessary for extremely difficult battles where victory is far from certain. Also, the higher the leadership ... the concierto of the AI might become even more sophisticated than your own ... or could simply hold to orders from the previous turn more aptly ... units could gain extra "battleplan" tactics slots, ect. I assume you could assign a whole wing, of several thousand, to a single battleplan, and then the individual soldier and unit AI would do its best to uphold that plan ... unless their morale dries up and they begin to falter or route. In which case even direct order do little ... you would have to dominate them with mind magic, blood magic, or necromancy/entropy for them to do anything during a route. Er, well perhaps some inspirational life magic (or inspirational air magic, or inspirational fire magic... ect. Just no such thing as inspirational "death" magic ... unless that "inspiration" is something more sinister)

It's nice that we will be able to to actually see the power of enemy (our) forces. While encountering 30 Phoenixes in HoMM5 would give me shivers, seeing 100s of fallen marching towards me, would be so much cooler .

yeah, I think I spent most of my time there lurking near the Stardock booth. just to note, if you really search through all the user videos of the PAX presentations, there is some discussion on it I guarantee. Just so you don't have to take my word for it.

necro. Hmm, I will use this opportunity to give a possible scenario.

10 adventurers/heroes, aided by a last-stand militia of 100 or so, vs an invading army of 2,000 low-level melee units. Who wins?

(my personal preference is for such forces to be relatively evenly matched ... unless of course the heroes have magical abilities, in which case the magic would gain the advantage)