Unless the highlight you're thinking of is very transparent, more like the light from a flashlight, I fear it could obscure intricate edges. Some have asked for even just a thicker path, but others have rightly pointed out
that that alone could interfere with visibility of the subject's edge. Or are you thinking that it stays the same width and changes color which we've wanted for years?
I think it might even be easier to simply allow users to select a custom color that will stand out against their image. Any color Adobe chooses for us will disappear against colors that are too similar.
Without a doubt, though, Adobe needs to do something to make our paths and Color Samplers visible to us against any background.