Imo the inconvenience people have with 8-bit color palettes is more about having to deal with color reduction and/or draw with limited colors in mind than with the final quality of the visuals.

People specifically looking to make a JJ2 tileset will know their stuff sooner or later. But it appears that experienced artists of this day and age willing to draw an episode cover image (like those for the community HH episodes) are alienated by the thought of having to deal with limited colors.

Personally, I think the combination of flattening and dithering, if done right, can give charm to the final result so I don't really feel the need for JJ2 to be compatible with 16-bit tilesets beyond these proof-of-concepts.