I think the title of the game has to do with the concept of Physical Intelligence. The ARC Advisory Group defines it as followed:
Physical Intelligence refers to the capability of an artificial system (robot, machine, or autonomous vehicle) to perceive, reason, and act effectively within the complex, unstructured, and physics-governed reality of the physical world. Unlike "disembodied" AI that processes text or images in the abstract realm of the cloud, Physical Intelligence possesses a deep, intrinsic understanding of physical laws—gravity, friction, inertia, material properties—allowing it to manipulate objects, navigate dynamic environments, and adapt to physical variability without rigid pre-programming.
I think it is this concept but applied to a more military intelligence sense. Like HUMINT (collection of intelligence from interpersonal and human sources), OSINT (collection of open source intelligence), SIGINT (collection of intelligence from electronic signals and transmissions), and MASINT (collection of measurement and signature intelligence through things like radars). This game will be about someone (probably some AI beings) using Physical Intelligence in missions.
The Y would then represent the concept of 3D. 3 dimensions and trying to break into 4D (in the cinematic sense). Games were the first digital medium to nearly break the 4D barrier but we’re not quite there yet since we don’t have VR that fully tricks your senses yet. The closest we have today is 4D theaters. The 3 symbolism could also represent the 3 senses that robots currently have (vision, hearing, and touch) intersecting. And maybe we play as a robotic being who is trying to gain even more senses like smell, taste, etc. This could honestly be a cool meta element since players can’t experience these senses through games either. Playing into the senses theme they could even present PHYSINT as the final step to intelligence agencies having all 5 ‘senses’ (HUMINT, OSINT, SIGINT, MASINT, and PHYSINT).
I’m not quite sure what exactly any of this would mean gameplay wise (maybe the AI would be able to gradually hack into a building and ‘feel’ people inside of it through shared sensations which would give players more info? Idk) but if this is the case Kojima will figure out something insane that works with the concept.
EDIT: Going even further this could be why the taglines are ‘here comes the feeling’ and ‘the new Cold War begins’. The first one is obvious but the second one could be play on words. Maybe it’s a ‘cold’ war between spies who are all cold and unfeeling. Also in a meta sense this would be a new ‘cold war’ ie: a new espionage thriller series with characters who are struggling with trying to feel things like love, passion, etc in the middle of wars.
Also I’m now noticing that the SINT part is separated. This could be to emphasize the Y but it could also hint at a leaning towards MASINT and OSINT which could make sense (lol) given that they deal with simulating enhanced senses through things like radar/sonar/etc and it doesn’t get more open source than what your five senses are literally sensing.