When it comes to the era of non-subscription MMO's, I'm more worried about monetizing nuisance than so-called "pay to win". The game either is or is not fun on its own merits, and for me personally it doesn't matter whether someone else is able to pay to get out of it. By contrast, non-subscription titles are far more likely to create inconveniences and nuisances and charge to alleviate these problems. This approach bothers me because it affects the quality of the game experience even if I am willing to pay the fees.
Case in point is Marvel Heroes' new "runeword" system. Largely copied from Diablo II, the idea is to collect random runes and enhance gear with them. The issue is where to store these items. DII implemented a total of 33 Runes during its run, but Marvel Heroes has chosen to launch their system with 38 runes and plans for "dozens" more in the future. Runes stack with other like runes (though this prevents you from dropping them on the ground to trade with other players - supposedly to be fixed in a patch later this month) but that doesn't do you much good once you've got 72+ different types of runes to stack.
The money in the system then, is in selling players crafting storage tabs in which to place all this new clutter. The price tag is for the most part reasonable - roughly $3 buys you a crafting stash tab that should solve your problem for the foreseeable future. From a rational perspective, unless you intend to just donate all of the runes to vendors for exp and credits (not a horrible idea in the short term for all but the rarest of runes), it's a no-brainer of a purchase. No doubt the developers sold a bunch of these things this weekend. And that's what concerns me.
The metrics are going to say clearly come Monday morning that adding over three dozen drops to the game dramatically increased their revenue on crafting storage tabs. By making this purchase - a purchase that is well within my means - I'm sending a message that every patch should add another several dozen drops (I'm not making that number up, the FAQ on the feature says that "dozens" plural of new stones are planned) and rewarding the developers for a decision that in my view adds clutter without adding fun or interesting gameplay.
The subscription MMO era was not without its dirty little secrets - the whole daily quest system was invented to make repeatable content take more real world days and thus more real world subscription dollars. Even so, I'd suggest that having a single payment model enforced a constraint that the game in its one pay-or-not state had to be fun. The monetary reward for doing something obnoxious - say, adding dozens of additional runes in the future rather than new recipes that use the existing runes - was less direct. With the new model, you can pay to store the stuff but there's no way to pay not to have dozens of items that are designed to be stored cluttering your inventory with each new patch.