I won't speculate as the name of the Elder One but it is possible we have seen a stylised representation of it: the Lyrium Idol. I'm thinking there could be a connection because of the presence of red lyrium on the surface of Thedas which seems to be erupting from the ground in the vicinity of Fade tears. The idol was clearly the image of some sort of entity that the people of the ancient thaig worshipped. Proximity to the idol or anything made from it, sends people mad, presumably crazy enough not to worry that a Fade rift will destroy the world. Essentially it fuels chaos, which is necessary to fuel the expansion of the rift. A small piece of refined red lyrium (as opposed to the raw stuff which is everywhere) is found on one of the Venatori. I wouldn't be surprised to find them everywhere that there is chaos. It has been hinted that it is no coincidence that all this trouble and unrest has occurred at the same time and that someone is actually behind it. The ultimate goal of the Elder One is to remove the barrier between the Fade and the material world, in which case, as has been stated by a developer somewhere, the demons do win. So far as I am concerned, in the world of Thedas, powerful ancient spirits/demons and gods are terms that are interchangeable. However, it could be an ancient elven dreamer operating through the Fade but located in that in-between world we see in Masked Empire.
Speculative idea: the elves were originally spirits that became material in the way that Imshael can, so they were magical and immortal. When Fen'Harel created the Veil they were cut off in the material world, so they lost their immortality and became truly mortal. This occurred around the time that humans first appeared, hence them being blamed. Then their magical gift got transferred to the human race through inter-race unions with the resulting offspring always being human. The ancient Magisters suspected the origins of the elves, saw them as a threat and in particular the seat of their power, Arlathan, hence them sinking it into the ground. They were aided by the demon spirits that had originally been opposed to the spirit elves and had been shut away within the Fade, whilst their original material bodies were trapped underground. Seeking their release, they urged the Magisters to enter the Fade but it went wrong. Now someone is attempting to do it from the other way round, so instead of mortals entering the Fade to release them, the veil is removed so they can simply walk out.