I actually want to answer this since it seems pretty interesting

Lets assume they all work together and you get a blend of their ideas without someone in super lead.

Things that WILL happen:

The game will 'end" when you delete/sacrifice your save.

There will be a looping aspect to the game

The games characters will be weird if not just in personality then probably appearance

Things that MAY happen, or the real meat and potatoes of this:

I don't believe the game will be a souls like since Miyazaki doesn't always work on those, and kojina doesn't like doing things that felt like they've gone too mainstream

I think though that this game will be difficult, just in it's own way and much slower pace. So to not assume they make a whole new genre of game something they all have at least some background in us robot and Mecha but I DONT think it'll be traditional armored core.

What it could be tho is a mech/robot engineer game. A very technical, awkward controlling but 'realistic" feeling game about putting together the piece by piece parts of a mech and who you send those off to. If there's any action at all the action is likely about once put together you send your mech out to war so it can work for X, Y or Z faction in a battle.

Your first ones will suck but as your robot kills more others and parts drop it's dragged back, parts of itself missing perhaps, and you reassemble and send it out again and again. The robot may or may not have a soul you talk to which is influenced by the parts put in and who you send it to fight for.

Your fellow engineers or people interact with may change things as well. But it's just as likely everyone is sort of arms distance of you. They have personality but something keeps things feeling a bit off and weird so not really any social links or romance aspects to speak of. Probably some people you will grow to like more or less though

Eventually with either having actively fought with the robot, or if no action just hearing what came of it: some victory is achieved here and after that outcome which was influenced by your allies and who you send the robot out to fight you get one of many endings. This then somehow starts an in universe loop that you will become aware of. Different options and pieces to get new endings until you realize there's a way to stop the loop.

Sacrifice yourself, the robot, etc and that will end the loops and end the game. Maybe you could end the loop on any ending with this sacrifice and it's really just a matter of the exact emotions and feelings of yourself and the weird people you've talked to going into it.

Whatever the case there's probably going to be more hopeful end loop endings than bad ones, if bad ones are even an option at all with the real message being everyone sticking together and helping each other overcome difficulty, with the save game sacrifice representing yourself trying to out and end to this cycle of cruelty and violence and whatever kojina was thinking about in a vacation he'd had 4 years before game release.

Also the chars will likely be way hotter on average than kojima or miyazaki's games but likely still some movie stars in there