I gave up on modding around 1.7.8ish I think, so this is good information.
I also agree that, by default judgement, Forge basically is the modding API at this point. But I disagree that blessing Forge as official is the way forward, precisely because of how tightly bound it is with the existing structure. How well would Forge be able to integrate with this new C++ version? Who knows! So, yes, use Forge as a primary input or even a starting point for a true official API. But don't just blindly bless Forge.
Using Forge as a starting point is basically what I meant. That has to happen if there is every to be compatibility with the existing mod ecosystem. Where future development goes from that point is another question. Forge itself hasn't stopped developing either, and they've had a focus on "fewer mod updates" for a while now (i.e. Forge properly isolating changes in Vanilla).
I also agree that, by default judgement, Forge basically is the modding API at this point. But I disagree that blessing Forge as official is the way forward, precisely because of how tightly bound it is with the existing structure. How well would Forge be able to integrate with this new C++ version? Who knows! So, yes, use Forge as a primary input or even a starting point for a true official API. But don't just blindly bless Forge.