Let's ask Trevis and Chris, the other two co-authors. There is significant interaction with #620. For example, #620 lets you warn on a use of GADTs, whereas #601 lets you warn simply about the presence of -XGADTs flag. (I am pretty doubtful about the utility of having both.)
I am pretty keen on at least establishing a Stable/Experimental distinction. I'm agnostic about how many other categories, if any, to establish.
The “Stability Goals” document is a bit more than just goals, it’s
actually a pretty clear policy.... But yes, we could ratify them and put
them somewhere useful. But why not the GHC documentation?
I advocate for incorporating them in the GHC Steering Committee process, not GHC documentation, because the rules GR1-3 primarily cover decisions of the GHC Steering Committee. That is, what changes do we accept? For example, we might be more willing to accept a breaking change to an Experimental feature than a Stable one.
Simon