I love the idea. I'm not a huge Total War fan. The last one I played was Shogun 2. They tend to get a little stale for me. But I love me some dark epic fantasy. So maybe this will give it the spark I want.
It's going to be interesting what they do with the campaign. They've always done these quasi historical settings. This is the first time for them with trying to incorporate magic and monsters. I wonder if there will be an actual storyline or if it will but sandboxy like the other Total War games.
An actual storyline would be anathema to what makes Total War games so good.
It would also be wasted resources, in my mind. The Joy is seeing if you can take over the (old) world by whatever means you feel most appropriate.
It would also be an awesome way to spice up the different races - Rather than all being pretty much the same, just with different starting zones, racial bonuses and initial resources, all the different races would/should play far differently (if done correctly).
This could go as far as some races not really owning cities, but appearing wherever they like, some spending most the time underground (how this would work?) and others playing more 'conventionally' with city owning, taxes collecting and peasants suppressing.
...I'm too into Divinity Original Sin 