It's already going away for me in a sense as I build up a library of AGENTS.md and Codex skills. I see no reason such things won't get baked in at the agent layer so that domain specific rules and such are automatically applied when appopriate.

Who's to say it won't?

Yeah, uh, why would it go away? In what world do you completely surrender your ability to control the work product, the methods for achieving said work product, etc. That is the dream of a PHB.