It's a raw bus? It's like an operating systems idea of a network stack being to hand all software raw ethernet access. It is an obvious concurrency disaster once you have more than one application trying to access it, the data transmitted and control handed over is entirely opaque to the operating system (god knows what monitor vendors sneak over DDC) and most importantly all of these are absurdly low level implementation details that are subject to change.

For all you know, they don't even need DDC beyond the initial EDID setup and multiplex the I2C hardware to do something else and can't physically provide this interface anymore.

They can. This entire article is about how they implemented it on M1 macs. Did you read it?

This was never an intended feature. If I understand the article correctly, they were using an undocumented ("private") API which happened to stop working.