Most of the issues originally described in this task have been resolved!
The only remaining problem is that the Weight Paint object is affected by shading options: lighting, material, textures, etc. It should always act as if the shading mode was set to Flat with a completely white color.
The colors of the weight paint overlay are meant to represent the value of those weights. If those colors are affected by anything else, the original information they were trying to convey is corrupted or lost. See T61486#702654 for illustration.
Hopefully this will be fixed as part of the Attribute Edit project.