I'm wondering if this is related to the recent Roku argument; perhaps YouTube is trying to force Roku to incorporate a hardware decoding chip (maybe with an increased cost) in future products as a condition to stay on the platform.
I don’t think YouTube cares if you use hardware of software decoding. I also don’t think they care if you use their hardware decoder or someone else’s. The issue with roku is they don’t want to include any extra hardware to support vp9, and they use such cheap/low spec hardware they can’t reliably decode in software.