Is Pantheon: Rise of the Fallen Too Niche of an MMORPG?

The developers of Pantheon: Rise of Fallen have stated that they're not trying to make an MMO that appeals to all types of people - they just want to make a high quality game for a specific target audience. And they've made it clear who that target audience is. But will that demographic be big enough to keep the game sustainable over a long period of time? It may be easier to predict than you think.