DISCLAIMER: WALL OF TEXT INCOMING
Some of these posts have touched on good ideas.
I will say from the start that I think it's very ignorant and pessimistic to think the total war series needs to be limited to melee combat and nothing else. Tactical combat aside there's so much more to the total war series than the actual real-time combat bits. Hell medieval 2 was already one of my favorite games and I hadn't even fought one real-time battle, I just autoresolved the conflicts: the campaign mode alone drew me in. The word total war isn't context or time period-specific, and just because it's been well-established in melee so far does not mean it can't evolve or expand. Empire was a big experiment and I'd say CA pulled it off incredibly well. Sure the 18th century isn't exactly a historical period that makes people wet their pants and the combat is quirky at best because most people aren't too familiar with musketeer formations, moving line infantry around and using them in conjunction with obscure, specialized units like pikemen and cavalry. But on the whole for those willing enough to invest time into understanding the combat, I being one of them, it was rewarding, challenging and fun, with each unit having its role to play in the grander scheme of things.
On the whole, I'd say the key issue at hand is the real-time aspect and not the campaign aspect because it's easier to modify the campaign aspect to suit the time period in question. In my opinion the campaign mode for empire was just as fun and addicting as that of medieval, if maybe a little less creative because they removed the fun quirky bits like angents and their attributes and the possibility of an operation backfiring on you but introduced other new aspects like the ability to reform your government or fight for monopoly of trade theaters. So on the whole I'd say the campaign mode is a non-issue and trust CA will always find a way to adapt it almost flawlessly to the time period in question and keep it fun, entertaining, and addictive...I do have some things I'd love to see IF a modern one were in fact to be made but I'll save those for another post.
So with that we come to the real-time aspect and a few people seem to grasp what would be the ideal concept but I'm surprised no one's even mentioned the one game which in my opinion almost perfectly pulls off the idea of realistic modern warfare in an RTS and that is world in conflict. Aside from the concept that you can only specialize in one combat arm as part of a sort of A beats B which beats C which beats A sort of triumvirate and the fact that the role of infantry was considerably insignificant, the gameplay was flawless. Camera controls exemplary, units moved realistically but fast enough to keep things exciting and the pace manageable, the command points for air support idea was almost cathartically fun making things like tactical nukes usable and worked perfectly, the reinforcement system put you in the heat of the action without the long chore of base-building, on the whole it was just an excellent game. The only thing it lacked was that because of the combat arm system and the reinforcement points limiting factor you could never really control a big, combined forces army...the most you could ever really control at any one point was either 5 big armor tanks, 5 helicopters, a couple of infantry squads with some APC's, or a couple of artillery pieces with some mobile SAMS for defence and that spoiled the big conflict feeling somewhat. Now take away that limitation and factor in the total war concept of colossal armies. All of a sudden you're leading an entire company or even a battalion complete with hundreds of men, tanks, APC's, arty pieces and off-map support, perhaps in a field, a city, or wherever the conflict leads you. Both sides adapt to the environment, take cover while shooting, call in air strikes which if well-placed could decimate half the guy's army and win you the game but also have the potential to just be a huge waste of resources, just like in CoH, units are specialized and deployed together as part of a combined arms force...dunno about you guys but that sounds like a spectacular fight to me. Add to that the profoundly detailed, realistic and fun and rewarding micromanagement of infantry which company of heroes had, with squads, snipers and weapons teams moving in and working together through cover, buildings and pretty much every environmental manifestation to accomplish a goal, capture a piece of ground or just kill some enemies, add in the tanks and vehicle support which company also integrated very well into the infantry play but get rid of the base-building element of that game, add in the wide area and excellent off-map support elements of world in conflict, finally escalate things to the total war scale with hundreds of units on screen and maybe factor in a few other good things from that game like the presence of a general or commander who inspires your men and bestows bonuses on troops and units and I believe you will have, what I argue and hope will become, one of the finest RTS's ever created. It would be extensive and cover every aspect of modern warfare in a way which integrates them all together as one big combined arms war effort of tremendous scale, from the cover and shooting aspect of the infantry to the armored blitzkrieg to the tactical off-map support element. All you'd need then would be a good HUD and interface system in order to allow actual control of such a large-scale operation, but starcraft has already pulled this off to an even greater extent because in that game you also have to worry about logistics and actually getting your units to the fight so I see no reason why it would be a problem. Combine all the above elements together properly and I believe you'd have a jewel of an RTS game which would be a godsend for the real-time element alone, not to mention how cool the addition of the incredible campaign element that the total war series is already famous for would make it...
Oh, and did I mention there could also be a naval combat element?? More on that in another post.
I apologize for the wall of text but this idea has been sort of my daydream project for months now as I'm a fan of knights and history but also love technology and modern warfare and believe it's been severely underplayed outside of the FPS genre.
I know there are a lot of things I haven't addressed but I don't want to make the post any longer than it needs to be. Feedback is more than appreciated, so long as it's constructive.