I would be very interested to know how good they are at tracking a user across brand new browser sessions. I have mine set to delete cookies, cache and history (minus a few trusted domains) on close but I’d imagine it would be easy to differentiate between me and others in my household by browser fingerprints alone. The only question then is whether those guesses are reliable enough for Google to essentially treat those sessions as 1 person, or throw it away since there are bound to be quite a lot of cases where 10s or 100s of people on the same IP have very similar browsing habits and configurations and trying to figure out who is who would be incredibly difficult (think offices where everybody could have exactly the same laptop and share similar browsing habits due to working for the same company). That’s my cope anyway. The alternative is Youtube over Tor for which would be painful.
Points 4 and 5 on my end are essentially two sides to of the same coin. I should clarify, I don’t have a problem with YouTube introducing a new feature and making that Premium-only.