And yes, it would be a great new feature (and I guess it wouldn't be extremely difficult to add it to the new grading tool). I've been using this method in other software and I must admit that it's surprisingly fast to finetune your clips to a neutral standard.
Is is correct to assume that grading becomes more important with HDR, the same way my AF became more important with UHD?
That would be correct, much more dynamic range/shades of color to work with. You don't necessarily have to grade it more than SDR to make it look good, but you have far more options.