Definitely not in the PHB. It's a very niche play style and, while I like that it hearkens back to D&D roots, I think it would really be a confusing addition to the PHB. I don't think it should be in the core rule books at all, even the DMG. It seems like something that needs a fair bit of detail to work, and so it should get its own book or else it'll just be another half-assed concept. And it doesn't really seem on brand for books that are overwhelmingly based on individual and party-level adventuring.
You could even make it into a separate game that links to the D&D campaign...which is where the concept originally stems from. D&D started with the idea that the heroes were being developed to integrate back into an ongoing war-gaming campaign.
