It's a short essay; there's not a lot of advice there, and Vaillancourt really never answers the question. But two things make it worth reading. First, Vaillancourt describes the advice she long gave to people who had asked her whether they should provide feedback, before a recent experience altered her perspective: Don't tell losing candidates why they lost, she advised. Tell them why the winning candidate won. That would have worked for me: It accentuates positives, but it also would have told me what I needed to do to succeed in future interviews.Vaillancourt goes on to describe a situation where she did not do her best in an interview, and received some frank feedback on her performance.
I think this could be (and should be) done at most companies that hire chemists; I'm guessing that it would not add to the cost of an on-site interview to send an electronic form back to the non-hired candidate that gave some short feedback. Comments on perceived technical skill, social/'fit' issues with the group that you're going to work with, comments on communication could all be written up -- you could easily imagine a multiple-choice form that would be sent back to the candidate, along with the (sad) rejection phone call or letter.
It's my hope that companies will adopt this practice, but I'm not holding my breath. Sigh.