"the human is a commander, so the units are intelligent in their own right (thus, handled by the AI); and the AI is also giving the human commander real-time advice based on what knowledge it can discover through the human's vision "
I see what you're saying. Yes, I daydreamed about such models too. I got excited about two games that stepped into that direction: Supreme Commander's dual-monitor setup with a macro, commander-like view plus detailed, micro view; Full Spectrum Warrior and Full Spectrum Command. The S.C. setup shows people are dabbling in interfaces that might lead to that. FSW and FSC are straight implementations of what you describe: commanders controlling AI agents that are semi-autonomous and provide feedback. FSC isn't available to public but is what I wanted more: limited commander view with data on your troops, position, intel coming in from video feeds or satellite, and so on. A hybrid model might let me go Harbinger and "assume direct control" of a character or team.
"I feel like that "human in the middle" configuration would actually make for its own new subgenre of 4X/RTS-like games, if we could get it right; "
It could. I'm not sure what it will look like outside Full Spectrum Command or bots in shooter games. A lot of the experience comes from the style of the people playing plus their quirks. The Call of Duty Ghosts AI shows that we might be able to approximate that as it did it so well I thought I was playing online against rookies lol. Most fun bots ever were.
"Come to think of it, this is what Dungeons & Dragons was originally supposed to be about, wasn't it? "
I think it was meant to enable and constrain the imaginations of players so the game took place inside their head. I never played it but it was a brilliant idea. Come to think of it, you're onto something here because games like Skyrim have all kinds of autonomous people doing certain routines or behaving in certain ways. There's even contractors and mayors. Any of these people could benefit from AI. Just a matter of computing resources. Could have one world where everyone plays the same world whose characters are controlled via a server farm at developer's location. I originally envisioned that for Runescape when I failed to get them to create a version of it for AI research. It would've been great for testing pathfinding, build systems, strategy, chatterbots, and so on. Skyrim more so.
Note: We could also test a collective intelligence where individual agents publish what they learn to central forums organized by topic. AI expansions could take time to periodically scrape that, try to understand it, and factor it into their gameplay. Basically, simulating player help forums that humans use. Additionally, could build superintelligences, gods, or advanced/E.T. AI's that tap into that plus much of world state that shouldn't be available. Even let them make changes to map or items with that dynamic factored in.
Lots of potential that might not have been explored yet but could make even simpler bots a lot more fun to watch. ;)