First let me say that it is awesome to see the anticipation for 2.0! I hope it is a sign of things to come and that FFXIV takes off for many years of success when it finally does drop. Now, about that timeline:
In your original post you quote Square Enix as saying:
Then you re-write this quote in your second post:a player must register his/her copy of the game no later than Thursday, May 31, 2012"
Registering and paying are two totally separate things. As soon as you install the game and start playing the free trial you are required to register. Even if you quite playing after your one month trial is up, and NEVER pay a dime to play again, you still "registered" your game when you launched it.must HAVE PAID for 3 months BEFORE May 31
Secondly, the 2.0 Beta is Free to Play, so they would not make you buy a 90 day subscription on May 31st then start the FREE beta a few days later. Therefore if you get 30 days free trial plus 90 day subscription for Legacy = 120 days total putting us roughly September 27th as the EARLIEST date they would pull down the old game and start launching the new game.
But, as we all know they are usually 1-2 weeks behind schedule on their patches (plus they probably set that date a little early on purpose to ensure ppl have time to get it in) so I would guess we are looking more at first or second week of October as the launch of 2.0.
Hopefully we will get some answers in two weeks at E3!