reply to Mersault
My preference: Apple implements the way everyone else does so it's predictable. At that point, after June 6th if Youtube performance is poor we can start complaining to TSI that they need better V6 peering to Youtube, for example.
This is really the only way V6 is going to get rolled out and done so with good performance. Falling back on V4 every time V6 is a little slow will just drag this out.