Nice post; very informative. I think the biggest reason I'm not too enthusiastic about the idea of having the Dwemer return is that it'd seem like un-doing major events that shaped the setting instead of moving forward into new things, like if they made the next Emperor in TES6 a lost decendent of the Septims or something.
Although that'd just be if the Dwemer popped back into existance just as they were. If it even was possible to return them, they could end up changed by the experience and be as different from the Dwemer as the Falmer are from the original Snow Elves. That could also avoid de-mystifying the Dwemer by having people show up who'd have been right at home in those ruins and be able to explain everything.
I agree that if the Dwemer would return, they would be changed by their experience.
I've been intrigued by the disappearance of the Dwemer, since Morrowind. They should never be a playable race though. It would not only go against established lore, but it would also reduce the mystery to a minor footnote in Tamrielic history.
There are many mysteries in the world (Big Foot, Nessie, UFOs etc etc). People are inspired by them, write books because of them, become explorers, just to find the truth. Yet, it's the mystery that drives them. Take away the mystery, life will seem a little duller for it.
I would love to read more books about the Dwemer, like I enjoyed reading about "The Fall of the Snow Prince" and the origins of the Falmer. Maybe the Dwemer lore can take on a more active part in the next TES game. Whenever I set foot into a Skyrim Dwemer ruin, I tried to imagine how it must have been, when Dwemer still occupied the building. The steam, the engines, the sounds... it seemed as if they had just left.
Plus, why would the Heart of Lorkhan be in Skyrim? I thought the Nerevarine destroyed it in Morrowind? Did we not use Keening and Sunder to kill it?