There seems to be a lot of theory-crafting around the web regarding why SWTOR didn't do so well. Maybe, just maybe, the real reason is because it just wasn't that great of a game.
Personally, I don't think the subscription model is dead; however, I do think that the subscription model will generally fail if a game simply is not good enough. Just about every attempted exodus away from WoW has always seen a resurgence back to WoW and its subscription model. So, I don't think the problem is people being unwilling or unable to pay for the game under the subscription model. I think it's more that they quickly find the content of every other game that has tried to dethrone WoW to be insufficiently compelling to hold their interest, or they find numerous unacceptable gameplay, game-design, and game-mechanical issues that ruin the game for them.
To be fair, at this point, it's almost impossible to unseat WoW. The game has been under constant development, refinement, and expansion for the past 8 years now. It is prohibitive for any new MMO to attain the same level of detail and volume of content upon release that WoW has built over the past 8 years. The idea of the WoW-killer was a potentially viable concept in the first 3-4 years of WoW's existence, but, at this point, the sheer size and scope makes any attempt a virtual futility for any MMO that simply tries to clone WoW's success. In my opinion, it would take a game that radically departs from the current formula, such to be incomparable to WoW, to have any chance. Otherwise, the only things that are ever going to kill WoW are Blizzard and time.