One interesting result of the latest blog war is that one commenter posted a link to the subscription numbers of Darkfall, including a timeline. Darkfall had 18,656 subscribers on November 17th, and now has 20,378 five weeks later. That translates to a growth rate of about 15k subscribers per year. So even if this growth rate keeps up, it'll take over 5 more years before Darkfall even breaks the 100k subscriber barrier.
As we were comparing that to Aion, I tried to find Aion subscription numbers. I couldn't find any current ones. 450,000 people pre-ordered Aion, and Aion held the top sales spot on Steam for a while after release. But I know neither at how many subscribers in North America and Europe the game peaked, nor whether it really shrunk by all that much since. I'm pretty certain Aion still has several hundred thousand players, but I can't find solid data for that. And of course in addition to that Aion is said to have 3.5 million players in Asia.
So saying that based on subscription numbers Aion is a failure and Darkfall is a success is stretching the truth to its limits. Worst case estimate for Aion is to have "only" ten times as many subscribers than Darkfall, with twenty times more being a more likely guess. Aion is a mass-market product, where the box sales alone made tens of millions. Darkfall is a small extreme niche product, which isn't remotely likely to ever catch up with the big guys. It will never even come close to rivaling a successful PvP game like EVE, and not even a supposedly "failed" game like WAR. Kudos for a small independant game studio to have produced a game that found its niche, and might even be profitable at 20k subscribers. But in the greater scope of things that is still chicken feed, and a failure. There are Free2Play games that make more money than Darkfall. The only significant thing about Darkfall is how rabid its fans are, and that is more working *against* future growth than for it.