I don't see the problem... You already have Dark Souls. What more do you want? New levels? New monsters? What is this, FIFA? Skyrim was a success because it wasn't just a remake of Oblivion, which wasn't just a graphics upgrade over Morrowind. They made it bigger and bigger, brought it to a bigger audience, then let the modders make the game as realistic and hard as possible. Anyone interested in a challenge just has to look for a couple of mods. Heck, I still play all 3 of them. The same will be with Dark Souls 2. If it fails, let it fail... somebody else will pick up the crown later, plus you still have the original. It's not even a niche game. You want to talk about niche games?
Falcon 4 was and still is THE flight sim to play, 15 years after being made. Falcon 4 FAILED at the time, and Microprose died because of it. In a world of Hawks, nobody expected better, ever. Then DCS A-10C came out and changed the sim world. In reply, some crazy geniuses remade Falcon 4 to be almost on par. That's NICHE. But a NICHE completely filled, more than you could ever need, just waiting for Oculus Rift. Flight Simulator was killed off, yet 7 years on people still play it like crazy. Want more? Anybody here played Orbiter? It's a phenomenal free game, but so complex that very few played it. Guess what, Kerbal Space Program took off based on it, but simpler, although again mods made it so complex that even the developers now have to adjust. In the meantime, many people switched to Orbiter for the extra challenge. Funny how things work, ha? Still in space, I still play I-War2, which is basically ancient. Who cares? It's still the best inertial space sim where you can go faster than light and zoom around stars guns blazing and all. Those devs also went extinct, but at least we still have their masterpiece to inspire the future devs.
These titles went all in. They failed, but we still play them many years after their demise. Now compare that with the Silent Hunter series which did the opposite. They started as a niche in the age of simulators, struck gold with Silent Hunter 3 (which many still play), then failed again and again to close that niche with more realism. They played it safe, failed, and we're left with prayers for a proper naval sim and imagination. The salvation might just come from the most unlikely place, Assassin's Creed (still Ubisoft). Once the masses get the taste, a niche game becomes a possibility.
So I say go all in... whatever comes next, at least you'll have a legacy. Dark Souls is not a masterpiece. Dark Souls 2 might just be. So good luck to them. Should Dark Souls 3 suck, failing to live up to the previous games, well screw it...