This is a similar way to which the UK superstruct festivals release their tickets. A VERY limited number of tickets for a very cheap price and then a big social media hype and campaign saying that tier 1 has ‘sold out’, even if there were very little tickets in that tier in the first place .
It’s an indication that the festival isn’t selling well as they will use it to their advantage to try and push day tickets sales and in my opinion the line up feels like 6 one day concerts at the moment compared to one 6 day long festival.
They don’t seem to be available yet though- I looked at trying to book a day ticket and they don’t seem to be released yet .
Personally I think Chappell is still more likely than Biffy Clyro cause she's more current and works better to cover the "pop" bracket. I can't see them having Paramore, Biffy Clyro, The Prodigy and Deftones all in prominent slots cause it's Glastonbury not Reading & Leeds/Download