Actually, i've given lots of thought to how it could be done.
First of all, regarding development time it could be something for a 3rd party developer.
Second and most important are the issues you mentioned about distances and numbers. In most cases when flying online, the action is centered around certain points. Let's also take into account the growth of IL2 servers in the numbers they were able to accomodate along the years. We've gone from 32 players to 64 and maybe even more (i've seen 60 or so people on a single IL-2 server and it was running just fine). I'm not entirely sure about this, but doesn't the current limit on IL2 servers stand at 128 players, with many of them running a mod that adds moving AI units on top of that (the same mod that will be included in the official 4.10 patch)?
It's not a stretch to assume that 5 years from now we could be having 128 players on a SoW quality engine, as the only thing that gets transmitted is positional data and maybe some speed vectors to assist in predicting motion and "filling in the gaps" in case of lag (which results in warping when the client ends up receiving the updated and correct positional data). The rest is handled client-side so the main limiting factor is usually how much and how fast your PC can render at one time and not the connection speed.
If actions are centered around certain points of the map with a total area of 100 square km as it already happens with IL2, it doesn't really matter if the map is big and a lot of it is empty. But what about the distances and the time needed to travel them on foot or with ground vehicles on a 1:1 scaled map?
Well, there is a solution to that but the only case where a combined arms sim would work that way is with a revised multiplayer mode, something like a dynamic online campaign. Imagine a persistent scenario that runs for a couple of weeks, just like a 3 hour mission on a dogfight server but longer. Aircraft already have spawn points on their airbases. Infantry and ground vehicles could have similar spawn points and they would naturally be closer to the front lines, in order to simulate the advance of reinforcements towards the front.
However, the best thing would be the ability to set up AI units in "travel mode" that you could then take control of. Say that i wanted to organize a tank offensive. I could make a few calculations and then set up an AI tank convoy, set the speed to 40km/h or something realistic for tanks of the time, specify a couple waypoints, a starting time and then let it do its thing. Knowing the speed and distance to cover we can calculate the time needed, let's say the convoy needs 8 hours to reach a certain point where the human players are supposed to take control of the vehicles. Since we could schedule the starting time, we could arrange the AI units to spawn on the right time so that after 8 hours the human players would be logged in and ready to take control of them.
As an extra cool feature, suppose we add the ability to password protect your units and an expiration time for this protection, so that people who don't know the mission objective don't take over your tanks and botch your carefully planned assault but at the same time allowing others to step in if some of the original players don't show up.With such tools, it would be entirely possible to set up offensives during the previous day and hop in the drivers seat the next day in the evening.
This is not limited in usefulness to ground units. It would come in handy for long range bombing missions as well, arranging them so that the players could take control of a B-17 formation just as they were nearing enemy airspace, fly the ingress, attack and egress parts of the flight and then revert the units back to AI control when crossing back out of the range of enemy fighters. I doubt many people would be keen to fly a 6 hour raid to Berlin, but having the ability to jump into a pre-made formation before the coast of the Netherlands and jump back out of it at the same point on the way back would probably cut down on the time needed to half. That's still 3 hours but it's not that much of a stretch, especially if we consider that most of the objective oriented DF servers for IL-2 routinely run 3 hour missions. Instead of flying multiple sorties lasting for 20 minutes to an hour on a 3 hour DF map, we could be flying a single 3 hour sortie on a two week online campaign.
Does this take development time? Of course.
Is it possible with current technology? Entirely.
Will it be a feature in SoW? I don't know, but i hope to see it in one of the future patches/expansions.
It is kind of encouraging however that Oleg Maddox has said in an old interview that there will be a new multiplayer mode, one that would enable servers to host scenarios with a longer running time. For all we know, the foundation for such a feature could be already built in the SoW engine and waiting to be enabled in a future patch
