I think it's pretty telling how many people thing that a real modern war wouldn't happen a certain way, or that the combatants would want things resolved without firing a shot. I hate to tell everyone this, but no one thought World War I would be like World War I, and everyone was really damn sure that we'd never let that happen again, declaring peace, outlawing war, and what did that get us? World War II. So, I think the important thing here is for them to be creative and surprise us. One of the big boogie men for modern conflicts is what keeps it from just going right to nukes? Well, why didn't anyone use chemical weapons in WWII? Hitler didn't because he was certain the Allies had a huge stockpile of it (which they didn't) and figured if he used it, they'd just gas the hell out of Germany. Chemical weapons aren't nukes, and they weren't ballistic missiles, but there was a whole, world-wide conflict that saw very limited if any use of what was by far the deadliest weapon that anyone possessed.
One concept could be a new age of empire where two or three blocs are fighting it out in different parts of the world, not unlike the cold war, but kick it up a notch or two. Yes, it means the poor third world gets to be the battleground like it has been since colonial times, but it's how things played out during the latter half of the 20th century. A more multi-polar or even non-polar world where the major nuclear powers are all under isolationist or neutral governments is another concept, or they could even do a Total War: Cold War edition that just kicks it up a little with regional conflicts and keeps the risk of total nuclear war in the background, and the goal is to pursue your goals without risking a conflagration.
Let's not pretend that we're somehow past the age of total war. People have done that time and time again, and time and time again, they've been very wrong.
So, on that cheery thought, bring on the good games before we're all consumed in nuclear fire!