Potentially as a way to justify how they lost their eyes when Blackreach (And Dwemer ruins as a whole) aren't that dark. Makes for a good story either way.
Possibly, but proof of such is lost to history at the moment. We really don't know what kind of culture the Falmer had before their downfall.
If there is retcon, it's probably the other way around. Falmer were supposed to be a myth one year ago. No one was able to tell if they really existed. The lore of the previous games made clear the falmers weren't the equivalent of the dwemers and didn't leave anything behind unlike them. So this game doesn't really contradicts anything except the fact that their existence is indeed confirmed.
I was so disappointed the first time I saw a falmer (in the mages guild questline, when searching for the synod). No one gave a flying **** about seeing falmers. I mean if was FALMERS. They weren't supposed to still exist !
I assume Falmer surfaced and made themselves known sometimes between Oblivion and Skyrim, but I wish we were the ones making the Falmer discovery ... This would have made an awesome questline, instead of making the falmer random creeps inhabiting dwemer ruins with only a couple of books of background.
The Falmer study book says that Falmer attacks are getting more and more frequent ... so maybe there will be something going on in the next games. Maybe the Falmers are going to go Dragon Age on the Aldmeri Dominion and pull a Blight.
If TES VI is Men vs Mer, we might have the Falmer (and Orcs) involved after all.