Hi, Mike. By starting this topic, you’ve added a feature request! We can all vote for it and comment on it. DxO staff will consider it based on our input and on whatever plans they already have for PhotoLab’s evolution.
For now, I only wish to point out that PhotoLab’s Selective Tone sliders don’t work the same as the similarly-named sliders in, say, Lightroom and Capture One. In PL, they have a stronger (in some ways) and even overlapping influence over the whole tonal range. (See here if you haven’t already.) After a bit of reading, I think I can see how a Whites slider would be particularly beneficial.