For me personally I don't enjoy the game currently so I don't play it at all, I still keep an eye on it but right now I refuse in using my time on something I don't enjoy and value enough to pay for. As such I would not pay for a monthly fee, if I enjoyed the game and could justify spending my time on it I would pay it without a second thought though, if for no other reason to support the game. I don't quite get people that say they enjoy the game, are still playing it 6 months later and still would not pay for it. Is $15 more valuable than your free time?

Yep, subs get activated, everyone leaves, the game becomes unsustainable and analysts predict that it wont break even in 4 years and the game dies and you've wasted money and gotten really angry! :P (Saying SE would never shut this game down ever is about as stupid as saying Sony wont get hacked... 3 times)
I don't think this is honestly true, if they started charging tomorow the people that would leave woule be a) the ones that will quit anyway when its time to pay, so no loss or b) the ones that would return and pay when the game comes upto standard anway. Honestly I see no loss from charging at all aside from lower player numbers for a while, but they are already at that point anyway.