It appears the festival is currently sold out, minus Monday tickets which are still available. It is not known if additional tickets will be put back on sale in the future, but for now, Saturday/Sunday tickets and 3-Day passes are off the market.
Last year was the earliest tickets sold out, with Saturday/Sunday tickets gone April 28th. This year is easily the quickest sellout, and a compliment to how loaded the lineup is top to bottom, especially considering the headliners are much lower on the commercial success scale than previous years.
Update: Monday tickets are no longer available. Here is my theory. The third level of tickets were to go on sale May 17. If they knew a sellout was inevitable, why not take the remaining tickets off the market, and sell them for a higher rate starting May 17?
Update of Update: The May 17th theory was when tickets were no longer available three weeks ago. The fact that the organizers recently said the festival is sold out means it is sold out. It will be a minor miracle if more tickets are released.