If you intend to integrate this to RTS (or vice versa) I think you should start with compromises when making a seamless integration.I think he means to make the city simulator element more of a meta game that serves a major purpose in the effectiveness of the RTS mechanics. You are right though, the idea of making the City Sim merge seamlessly with the RTS portion is a rather daunting idea. My aspiring goal is to create a game that's high in depth and complexity, but simple enough for a vast majority to pick up. As long as the mechanics are simple enough to understand, the general idea of the game becomes less stressful.
This is why I think Impression games style is more suited, although the primary reason of why I adore SC4 is micromanagement, you should avoid too much detail imo.
It is manageable in a game solely made for it but if you integrate other genres, it becomes more of burden. I don't know you , but I even can't handle farms in AoE in time when having a noticable fight.
Everything in the realm of possibility is within our grasps. The only question is how far we're going to reach.