Mordremoth theory
That’s not exactly new. The whole “sylvari=dragon minions” theory has been around longer than we knew of Mordremoth. And as folks have looked more into Mordremoth, the more folks have thought that there could be a tie to the Nightmare – though I hope that the thought of “all sylvari=dragon minions” has diminished somewhat, since Mordremoth only shows possible ties to the Nightmare Court among the sylvari.
Stop treating GW2 as a single story. Each Season and expansion should be their own story.
From all the lore stuff I have read it seems there is plenty of reason to believe the nightmare court has nothing to do with mordremoth.
I can’t imagine the asura experimenting on some/one (idk which) of the firstborn sylvari would have been pleasant experiences, and riannocs death and betrayal at the hands of someone he trusted could both have introduced darkness to the dream.