But the thing of it is, a lifetime sub is just not a good idea for a variety of reasons.
I mean, if the game is a huge success, then the people who paid a lifetime sub will not have to pay another dime to play an awesome game. Good for them. But what about the people who made the game? That's money they will miss out on as payment for their efforts, or even to invest in improving the game so it gets even better as time goes by. And if the game is a flop, players will have paid a huge sum of money for a game that sucks. Sure, it might help SE pay off some investors and help them break even and whatnot (though let's face facts here, it won't, because not a lot of people are going to pay a huge lump sum of money for a lifetime sub to this game), but it will leave players who paid that money with a bitter taste in their mouths, and chances of anyone who in't a blind SE fanboy ever investing in another one of their mmos afterwards would be slim to none.
And let's not forget that even offering a lifetime sub to this game would not do much to instill trust into the players. It would be seen exactly as it is; SE offering a payment option that might help them break even in case the game doesn't do well. Which would look to players like they were anticipating the game being a failure and are trying to cover their proverbial behinds in such a case.
In comparison, that would be like being on a cruise ship with a bunch of other people, the captain telling you all "You guys are gonna have so much fun!", and yet finding out later that all the lifeboats are labelled "For Captain and Crew only". You ask the captain why that is, and he tells you "Well, we couldn't fit enough lifeboats on the ship to carry everyone, so we felt it best that we just make sure we have enough to save the crew and myself, you know, just in case. But don't worry! We planned our sailing route months in advance! So in all likelihood, this ship won't sink! We should be fine!" Would the captain's reassuring words make you feel better about the situation? Or would you at least feel a bit, oh I dunno, on edge? I don't know about you, but definitely the latter for me.