The undo feature is really useful, but sometimes I think I changed something I didn't mean to change when I click HSVs or HCY' and the color flashes on the grid, so I hit Ctrl+Z and the color I thought I accidentally changed goes away. A "Redo" button would be nice as well so that we can undo an undo and perhaps A/B a decision.
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Gamut Masking is an interesting feature but it doesn't work the way I would expect a gamut mask to work when in a rectangular hue transform. It would work in an isometric view of an RGB cube with the white/black range aligned to the camera, I've seen this setup used to map out the gamuts of paintings based on the corners of the plotted colors to find the pigments used to blend into all the plotted colors, and I've done this myself with Team Fortress 2's color palettes to extrapolate potential "primary" pigments. It would also work with an xyY chart with the camera aligned to Y since additively blended colors form straight lines in these, and this would make gamut masking viable with LAB and JzAzBz if you were to convert the points in LAB / JzAzBz to xyY and interpolated between the points on the gamut mask within xyY and converted the coordinates back to LAB / JzAzBz so that the gamut mask curves to show the actual gamut of light blending together instead of just a "perceptual gamut" from gamut masking directly onto LAB / JzAzBz. Though there's bound to be cases for both transformed and non-transformed gamut masks on LAB / JzAzBz.
Said RGB Cube:
An additional color generation method could possibly work in the way I mentioned earlier with finding potential pigments of a group of colors; find the mean or median vector along colors of a certain similarity to each other, follow the vectors out to where they overlap, and use the overlap coordinates as colors to blend together to make new colors in the palette.