I have to admit, I'd be kinda salty if I was asked to leave a flight after I'd boarded - even as standby. I know how it works, I'd have no real room to complain, but I'd be irritated as well.
I'd complain about it in a lounge thread. I might even fire off an email to CS because, ugh, all of a sudden I'm back to being heavily delayed and that's irritating too.
Then I'd get a $100 voucher and be completely shocked, a little chagrined, and grateful. I'd have to say something nice about WN in the lounge thread.