I must admit that the name “Generalized Hyperbolic Stretch” (GHS) is a bit intimidating (this name isn’t mine, but that of the authors). But ultimately, it’s the internal mathematics that are complex (I’m in awe of this mathematical masterpiece… they’ve managed to combine, into a continuous system, a series of hyperbolic functions more complex than Sigmoid alone… who doesn’t know Sigmoid?), more so than the actual use (once you understand how it works… the lack of accessible documentation is a real drawback).
Thank you for this review and your contribution. 
I’ll soon be starting a thread about improvements to ‘Game Changer’.
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Slightly improve CIECAM (Color Appearance & Lighting), which remains, in my opinion, the Rolls Royce of CAMs (Color Appearance models), by allowing hue rotation and saturation variation for each R, G, and B channel. Why reinvent the wheel? The latest version dates from 2020 and has very few shortcomings… The researchers’ work began in 1997. Admittedly, it might seem like a few things are missing… nothing is perfect.
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Allow the “Primaries & illuminant” Abstract profile to vary primaries in polar coordinates, rather than linearly: it’s a bit more intuitive… but just as tricky to use… like anything related to primaries (regardless of the software). Be careful with imaginary colors and exceeding the gamut.
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Add two matrices to ‘Stretch Settings’. In addition to ‘none’, ‘AgX’, ‘JzAzBz’, and ‘Cat16’ (the latter three working in RGB mode), I added JzAzBz and Cat16, these 2 models in XYZ mode, which is at least theoretically more rational.
Thank you again
Jacques