Sakkura :
WoW subscriber numbers are currently increasing. EVE Online subscriber numbers are also doing well. Your claim about subscription models being unsustainable today is quite obviously incorrect. Just because Rift, SWTOR, Age of Conan etc. weren't good enough to sustain a subscription model doesn't mean no future MMOs will. If the game is good enough, people will pay.
But WOW and EVE are dinosaurs, having launched back in the early 2000s - the golden age of all MMOs.
As you surely remember, back in the time there were only few online games /apart from good old MUDs/ worth playing - Everquest, Ultima Online and Asheron's Call... Everquest has now gone mixed mode - f2p /limited/ and sub /for all access/. UO has many shards around the globe, AC and Lineage... dunno really...
It was in the early 2000s when many of the best mmo games saw the light of the world - WoW, Lineage II, Ragnarok, Second Life, Eve... Back then was a subscriber model pretty much acceptable. Till Maple Story tore it down and showed that a game can be f2p and still generate revenues...
And there was Age Of Conan - probably the most bugged game since the release of Daggerfall. Missing zones, missing quests, no endgame... Extremely frustrating... And it took whole 3 years to fix those issues. But the trust in the game is even now in the pits. And this is the proof you can not build a MMO on lore alone - the gameplay is important.
And here is ESO - the game in which I wasn't able to play for more than an hour without discovering another bugged quest, inaccessible area or got the "unexpected error" message. The game which zone messages were flooded with: "Is the <quest name> bugged?", "How can I retrieve the staff?" or "I'm stuck in <quest name>, what now?"
People will pay, people will get angry and the game will be forced to go mixed /like AoC or EQ/ or B2P /as many others/ with an in-game real currency shop.