I hardly think the subscription will be an issue. WoW, arguably one of the most defining MMORPGs, subscription-based or otherwise, has maintained a subscriber base of millions for over nine years. Another notable example is EVE. In my opinion, the biggest obstacle for any MMORPG is originality. Everything from game mechanics to the UI have to be simple and generic enough to be easily interpreted (especially in combat), and yet must be unique enough to set them apart from other games in the genre. Story is also essential, and delivery is especially important in an established universe such as that of Warcraft or The Elder Scrolls. Fans of a particular universe, or those delving into a new universe, expect a high calibre of story delivery and depth in MMORPGs. This, I would assume for a large majority of players, is especially important when subscriptions are involved. PvP is also expected to provide an immersive experience, and is expected to be balanced such that no character class has a decisive advantage over another. Many players (from my experience) dedicate themselves exclusively to PvP, so having PvP content on par with PvE content is important. The list could go on, but the point that I am trying to convey is that subscription fees are irrelevant if the quality of the game is such that the fees are necessary to maintain the game's quality. TL;DR: Subscription fees are the least of your worries.