I'm envisioning "D&D Super Real" - in depth combat, physical, and social system add ONS for the player who needs it.
* Combat is now down to 0.1 second rounds to minimize the discrete-turn-taking oddities and to allow for super accurate defense maneuvers (knife vs. sword vs. pike vs. bow at different ranges become plausible when the characters move 1 meter per round or less). Also featuring armor vs. weapon tables and wound charts for bludgeoning, piercing, and slashing. Yes, wounds, hit points and AC are finally split into dozens of wound types, four types of exhaustion, multiple defense maneuvers, and three armor ratings for each body part. Know exactly what the encouraging warlord, skillfull medic, and miraculous cleric can fix, and how long recovery times are. ("Ooh, sprained thumb from combat and foot fungus from marching... the death spiral starts unless you find a magical healer! No, seriously, let me describe the penalties and how long natural healing takes.").
* You have 10 different physical attributes and 10 different physical skills (each with subskills) that allow you to get reasonably accurate results in all major Olympic sports and adventuring activities (Climbing a rope with only your legs and off hand? We've got a number for that. Movement rate in stiff leather boots, with a slightly off center 50 pound pack, sword out, after 8 hours of adventuring, and not willing to risk significant exhaustion? We've got that!").
* On the social side, to use their backgrounds (like hero of the people) or skills (like streetwise) the player has to help the DM by providing needed details on the spot - what heroic things in particular touched this villager's life, tell me about the local barista and how well you tip and what you chat about for that streetwise roll. "If you're not going to describe your cousin's relationship with their boss and the security guard, at least give me more about their personality so I can work out the reactions. Oh, and I need all their stats, sleep schedule, and work hours too." etc... "So, this is the market you usually shop at. You tell me the availability and prices. Let's start with grade A large brown organic eggs and go from there. By the way does the egg merchant have a family, and how are they?"
Once you've mastered it, it's even more realistic (well at least more interesting) than life!*
* But we're not monsters. No need to track ammunition or damage to armor, and we'll never put your characters acquaintances in harm's way unless you say to.