I talked to the service manager at the dealership where I bought my 2017 WRX and asked about rev hang. Apparently, no one has ever brought this up to them So I have an appointment this evening to drop it off and have them check it out and get Subaru's opinion on it. I'm also going to drive my car with a tech on board and point it out so they can't say they couldn't replicate the problem. Let's see what happens. In the mean time, they're giving me a loaner until they get it figured out.