Hello,
I got the same issue here with 16-bit TIFF images. Using 16-bit colors for vertex when we use 16-bit images as input does make sense, but it would be nice to have the choice of exporting as 8-bit if needed.
This would be especially useful when exporting from Photoscan to Sketchfab : right now, it seems that Sketchfab does not support 16-bit vertex colors. Cloud points are therefore displayed with wrong colors. (I'll ask them if they can do something about it on their side).