I don't see them changing their model unless hearthstone and heroes creates a steady income. Then and only then (multiple profitable F2P games working for them), we may see WoW go F2P to attract all the people who used to play, which if we believe their claims, that would be around 20-30 million ex-subscribers.
There is something people forget as well. A well designed F2P has the ability to sell the items you buy in game. We've seen this tested before on one of the items (guardian cub mentioned above?). What this does is create 'whales' who have tons of expendable income and want to support the product they love. This happens in all the F2P models, but SWtOR with the cartel packs and unlocks are a great proof of how well that works for profit. SWtOR is a good example of how to do the in game store, and an example of how not to do restrictions (though it keeps getting less restrictive).
All Blizz needs to do is make a majority of the mounts and pets (and whatever other in game items they'll offer) sellable on the AH ... or able to buy credits and offer it for gold like Rift does (I think). What that does is allow people with in game currency equal opportunity to anything that people with lots of real life money do. It can actually be more profitable than a flat $15/mo. Some people spend $100s a month.
F2P does need a constant cycle of stuff available. It needs to be high quality (value). It needs to be desirable. Some niche, but mostly mass appeal. Transmog could be taken a step further; since they claim they can't implement dyes; they could simply recolor gear and put it up in the store for a reasonable price; a profitable substitute (that will attract forum rage, but what doesn't these days?).
I really think it has a good shot at working better in WoW than any other game; I know a lot of people who are unhappy enough for various reasons to not pay for a sub, but would play if it didn't have a sub; that in turn fills the world up more, atmosphere, full servers, more people spending money on the AH supporting the whales supporting the game.
People love being negative and hateful; but it doesn't have to be that bad. Blizz isn't EA after all