I don't see why sequel for Amnesia would be out of the question, but it would probably require some brainstorming regarding the story of Amnesia -> Amnesia 2 and some other stuff.
Even though I hope in their next game there's no annoying lantern as few times I had moderate frushtration of wandering in completely dark areas just because the lantern uses more oil than half of the modern world combined in few seconds and you can't pick individual candles or even torches (presuming it's one that is not bolted to its place) to use as limited source of light. It was same with Penumbra actually regarding the flashlight, but atleast in those games you had some sort of freebie source of light avaible.
Now I am fully aware that the way the lantern worked is part of the atmosphere and due the game's nature I am not too picky about it, but I'd rather have truly scarce oil that actually lasts for a while (and with scarce maybe 2-3 bottles in the whole damm game
) rather than one that eats more oil in few seconds than entire F1 racing weekend and some other optional (yet limited and possibly unreliable) sources of light.