They already lowered bitrates for non premium members.
Edit: I did some searching. In addition to that, the only relevant news I could find were about Google testing locking the 4K (2160p) resolution behind the Premium doors, which they ceased doing.
But it seems I'm mistaken [1].
[1] https://www.theverge.com/2023/2/23/23612647/youtube-1080p-pr...