A co-op superhero game but instead of playing as Batman and Robin, you're playing as Batman and Alfred. One player would fight crime and traverse a small open world without any kind of map or waypoints available to them while the other player has access to maps, public and private records, and other information that they must relay to the other player to aid in navigation and environmental puzzle solving.
This game would play like a cross between Batman: Arkham Knight and Keep Talking And Nobody Explodes.
Will there be a coop boy wonder buggery minigame?
SLEEPING DOGS WITH WARRIOR MONKS
The reason the Orient has so many martial arts, I've heard, is that Buddhism demanded its monks learn non-lethal ways to defend themselves. (Then they went and invented Buddhist jihad anyways, especially the sohei of Japan.) I like the idea of a game, open world or linear adventure, where you are a Buddhist monk (maybe Tibetan) on a pilgrimage or something and there's tons of combat, but it's all non-lethal, break bones and knock people out but you don't kill them. I compare it to Sleeping Dogs because of the idea of riffing on kung fu movies, this would just be drawing from the "warriors walking from village to village" type from WAY back instead of the crime thriller stuff that came later.
PIRACY AND CIRCUMNAVIGATION
I know I've talked a bit about piracy games here and there, don't think I've done so much here. I've only ever seen two piracy (not counting adventure-type stuff not focused on ships, and Pirates of the Caribbean knockoff games which were awesome) games that looked worth a damn, one Sid Meier's and one Black Flag, both with different focuses (more of an RPG game with emphasis on a reactive and living world, more of an action game with third-person adventuring on land), both very good in their focuses. Nobody has made, though, even as an indie game, a piracy game solidly focused on the simulation of a ship and its crew.
Sid Meier's kind of has some of it, because you have to provide provisions (in the form of a single composite food good), you have to manage your crews morale and deal with conflict over when to divide the plunder, and you have separate sail and hull health. Also, you can choose which ship. Beyond that, there's nothing to it. Officers are just basically collectibles that confer a stat bonus, there's no internal crew management, and nothing else really.
This is a bit of a shame, because pirate ships were fascinating political environments and the mere act of keeping the ship afloat is a whole story in and of itself. A game could be narrative driven and have the officers as characters (rather than just the First Mate being the only character in Black Flag; Sunless Sea did have, in a presentation with no acting, multiple characters for each officer position), or it could have them be more generated characters-as-a-bundle-of-traits-and-events approach. These have different strengths, one is better for emergent gameplay, the other for strong narrative (imagine the strong bond between Captain Aubrey and his ship surgeon Dr. Maturin, for example.) Politically, pirate ships were democracies that lived and died by a constitution. Crewmembers should absolutely be able to influence a player's command decisions by having (contradictory) preferences and being able to rally behind strong leaders to launch mutinies. If the captain is a naval commerce raider, on the other hand, they have to deal with naval regulations, politics of the officers' club, and access to brutal punishments.
I want my pirate game to both let me lash and keelhaul people to torture them and to have a minigame where you GET keelhauled (avoid the nasty, knife-like barnacles on the underside of the ship and mash that button to hold in your breath).
Ships should have systemic damage. At a minimum, I see defining the rigging, sails, masts, and hull all separately, and adding powder magazines and rudders as special systems that can be knocked out for massive damage/to disable steering. Rigging goes down, low maneuverability. Sails go down, low speed. Mast goes down, it takes its sails and rigging with it (these are harder targets, so taking out a mast is to sails what powder magazine is to hull, it's just a lucky/high-skill move to end it fast). A more simulationist game would have different sails interact with a real physics system to propel the ship, but real world sailing is slow as shit and unfun so I don't know that I'd want that. Hull damage below the waterline should cause flooding that raises the water level at a rate net of your ability to bilge, and if it goes on too long you sink (no ship blowing up miraculously).
Ship damage would then be repairable (to different extents) at sea, when careening the ship, and in port. Careening is when they would literally take a ship and run it aground and then kind of pull it with ropes to get it out enough of the water that they could clean its underside and patch it up as needed, possibly cut wood for the purpose. In these times, the crew might also go hunting for provisions and have festivities.
Weapons should, rather than just being number of cannons, be different types of cannons (Black Flag didn't let you make choices, just upgrades, but this was something it did well in having fire barrels, swivel guns, mortars, ramming, and regular cannons all be weapons). There should be different calibers, types of barrel, type of action if it's set late enough. I like my swivels. I like the idea of having sharpshooters (as was historical) up in the rigging and crows nest. Tons of melee weapons and traps (like caltrops) to be used in boarding actions.
Diving bells from Black Flag were sick and so would it be if you could dive the sites of ships you sank to get access to the goods that would not spoil in water (like jewelry and specie), and respawning diving
RIP in Skull and Bones, it sucked before it was ever even announced
MORE OUTDOORSMAN SHIT
There's two niches, in somewhat different directions, of hunting/outdoorsman game I don't think have been served yet.
One is even more simulationist, so like if most games with hunting were COD and The Hunter and such were Battlefield, what woudl be ARMA? There are probably good reasons to have tracking automatically light up where the footprints are, because sometimes looking at a 2D screen from a distance makes it much harder to appreciate nuanced differences than you could see in real life in 3D, especially with the ability to easily stoop over thing as you look at them. Similarly if the feces are mostly distinguished by smell, that's not something you can really do but just tell the player how strong it is. But you don't necessarily have to tell the player what speed the animal was moving at if they can infer it from the space between their prints, and I don't have to see it flash up that it was a moose, because what the fuck else would make a moose print. Other stuff that's more on the simulationist end includes having, instead of dedicated "this is where the turkey live" spots, having to infer it from the presence of things the animal is attracted to (a certain kind of berry) or actually finding specific damage the animal does (rabbits, for example, should have burrows that are noticable).
So basically, a game where the hunting doesn't lead you by the hand at all, everything you have to figure out as a detective. (These principles could just as well apply to detective work and tracking humans.) Additionally, I think it makes sense that in the hunting game I play you don't have to even skin an animal, because you're just returning it to outside the park. But if it's more of a frontier or survivalist type setting, then minigames to skin and dress the animal and potentially even make things from it (like leatherworking and taxidermy) add a lot to the experience. If your game is based around making individual kills feel very significant (extreme long payoff), it makes sense for the processing of the animal to be treated as part of that instead of an immediate comedown of just moving on to the next moose.
At the opposite end thematically but not necessarily mechanically is going cozy game with it (some of these hunting games can be very cozy), isometric perspective, very nice stylized graphics. Take the Lonely Mountains Downhill for example, a wonderful aesthetic:
Just you and your bike - take it on a thrilling ride down an unspoiled mountain landscape. Make your way through thick forests, narrow trails and wild rivers. Race, jump, slide and try not to crash - all the way from the peak to the valley!
store.steampowered.com
Slap similar mechanics on that but in that same perspective, add in some narrative, and you've got a solid concept for a game that does the same kind of thing but feels like an indie instead of a AA niche product.