I've been playing around the last few days with Company of Heroes and it's a fine game in a number of respects. While it's not 100% historically accurate, it does fine within the parameters of the game as defined by the designers. The AI seems pretty decent and there's plenty of tactical challenge within the game system itself -- I found myself making good use of suppressive fire and manuever to take out German positions, defense in depth and using AT guns to ambush German tanks.
The downside of the system is what plagues the majority of RTS games: pre-scripted missions in a linear format. This is by design as well -- there have been a few games which were non-linear in a campaign mode a little like the Close Combat series, and have been well-received, but most are not particularly interested in simulating a historical military situation. (I found Battle for Middle Earth 2 to be quite fun in this respect)
Close Combat, on the other side of the coin has some problems as well, including the 2d format and the fact that it's a ten year old engine that's been patched and modified as time goes on. It was excellent for the day, and is still fun, but it's showing its age. (before anyone lights the "flamethrower," I'm planning on buying and downloading CC:WaR in a few days!) However, using the strategic/operational system to generate tactical battles that affect the larger scale is a great idea and works very well indeed in numerous other engines such as the Total War series, as well as the CC series. Plus, people seem to really like the marriage of the two (I know I do).
So, I'm proposing a new design which would essentially be a marriage of the two systems -- a solid 3d engine with a 2d strategic layer which can accurately simulate a historical campaign of varying scale and historical period where players fight across pre-designed 3d battlefields. To that end, here's my tenative list of requirements:
Allow a player to fight across a board map with numerous units or a linked (or random) series of battlefields with a single unit (say, an infantry company 1944-1945 in NW Europe).
"Default" campaign mode where a player fights numerous battles across a campaign map similar to CCIV/CCV.
Live multiplayer via the Internet. A nice to have would be multi-multiplayers.
Area movement with units, represented on whatever scale a designer wants, both in terms of time, unit scale, etc. This would allow designers to represent anything from the Bulge or Stalingrad down to maybe something on the scale of Carentan (if it would make sense). Overall unit type may affect movement rate?
Support for land, air and sea interaction, with the latter two elements being somewhat abstracted. Some areas where I think they would matter would be interdiction of movement or reinforcements or aerial recon around the battlefield in addition to providing direct support during a "scenario."
Attrition, if it makes sense in the scenario. Varying resupply levels. Supply situation may affect battlefield morale and readiness (need to be able to simulated isolated units)
Weather effects on campaign movement, air support, attrition, etc. If scale is large enough, simulate weather fronts and temperature variations.
Scriptable event support.
Fully 3D battlefield, especially with complete line of sight support.
Infantry units can enter buildings. Tanks may be able to damage/destroy some terrain.
Buildings and terrain features themselves can be damaged or destroyed (walls, bunkers, trees, headges, etc).
Vehicles have different armor based on facing, etc.
Heavy weapons need to be deployed. Guns can be towed, or emplaced (on setup)
Mines, mine clearing, etc.
Fires, within reason -- a building gets hit with a flamethrower and can burn. If it burns, anything burnable nearby can also catch.
Capturable locations and set up zones on a map that vary based on unit location/previous possession, etc.
Numerous unit attributes...maybe not try for a ton of units on a map, but detailed units?
Flying units (helicopters come to mind for a Vietnam/moden version)
Variable size maps on the strategic and tactical scale both. Map creation tools allow for modifying 3d terrain.
Ability to place nodes that the AI can intereact with. For example, if there's a strategically important spot on the map (hill, bridge, etc), the AI will either try to defend or attack that.
Put in "mud zones" on a map or other effects based on weather. Eg, if it rains for three days straight, a field turns to mud. Ditto for frozen ground/snow. Or, have a basic map and overloads which depend on weather type (eg: zone_31_mud extends zone_31, etc).
Ability to script AI for a campaign and to instruct it for a battlemap. AI is linked between campaign and battlemap based on various factors (ie: the AI tries to create good matchups based on the location terrain type, overall battle situation, etc).
Designers can create new units, buildings, vehicles, etc, with a little 3d modeling work. (might be possible to create a community-based content exchange)
Designers should be able to create battles from ~1900 to near future. Most users would probably be interested in a WW2, tho.
Anyway, those're some of my thoughts on the subject. Some of this is subject to issues of complexity...particularly creating a 3d map and the mapping tools needed to build a battlefield, although 3d graphics programming is getting to be a mature field. AI is another concern...I know people mention that no AI can stand up to a human opponent, but not everyone is interested in multiplayer all the time. (I find it to be less relaxing, myself) Bad AI has killed more than a few games... Animation of soldiers would be time consuming, but careful design would mean it would need to be done only once..
I'd be interested to hear some thoughts on the subject, particularly from those of you who are also software developers. Not really thinking about any commercial model or actually coding something like this yet, since it would definitely be a pretty large effort with a dedicated team. Not sure also of what tools would make sense...I work mostly in .net. XNA?