Implement something like "Principled parsing for indentation-sensitive languages"

[Principled parsing for indentation-sensitive languages](https://dl.acm.org/doi/10.1145/2429069.2429129) [[pdf](https://michaeldadams.org/papers/layout_parsing/LayoutParsing.pdf)] lays out a way for extending parser generators like Happy with the ability to directly deal with indentation-sensitive languages like Haskell. The paper mentions that a patch was made to extend Happy with this functionality, but afaict this was never merged into Happy.

Why hasn't this yet been added to Happy? Did nobody have the time to finish off and optimise this work, or is there another reason?