I just noticed in the Local Adjustments tab I can refine the luma and chroma sensitivity of control points as you can for a control line so you can create a predominantly luma or chroma mask. I rarely go to this tab so this feature might have been there for a while.
I do wish I could drag the adjustment options off screen. I find them intrusive, even when using SHIFT-E. I also wish there was some was to turn off mask display when brushing.
On balance glad I upgraded to PL5, but I still go back and forth with CO21, which for me has better color control.