Haha, you have scooped me by about 1 week I am about to announce a project which will hopefully lead to a new Haskell report pretty soon, you just have to wait a few more days.
I think trying to bring GHC 2021 or GHC 2024 into report form is way too hard to consider as a single step. The user documentation in the GHC user guide and the GHC proposals is nowhere near precise enough to serve as language specification. One of the reasons the current Haskell 2010 language report can be somewhat concise is that it “cheats” by handwaving a lot of technical details and by referring to “standard techniques from Hindley-Milner type inference”. If we want the language report to cover features such as GADTs, type families etc. then we can no longer rely on this shortcut and have to rewrite large amounts of the report from scratch and explain all the technical details. The result would probably look much more like the papers Practical type inference for arbitrary-rank types or OutsideIn(X): Modular type inference with local assumptions - Simon Peyton Jones than the current report.
(Something I had in mind myself was perhaps resolving at least some of the points where GHC’s
Haskell2010
and the Haskell 2010 Report differ - Section 16.1 of the GHC User’s Guide. For each difference, it is possible to ask “Which is better: what GHC in fact does or what the Haskell 2010 Report provides?” In some cases, the answer to that question may be ‘clear cut’.)
That is more or less precisely what I plan to do: A revised version of the Haskell 2010 language report that takes account of how the language has changed in the intervening years is a feasible project that can be achieved in a limited amount of time. GHC currently can’t compile any non-trivial Haskell 2010 programs, which is really a quite unfortunate situation. I think we can try to fix this problem first.