One fine day, Nikolaus would go "For the greater good"
Gee, now there are 2 ladies vying with Nikolaus for the dark lord position? How precarious
It seems rather weird for Nikolaus to follow Grindelwald's path as they have never met and certainly the reason is not simply to continue his legacy.
Right now, my plan is to have Nikolaus learnt about Grindelwald through Aberforth instead of what was mentioned in text. (Nikolaus was from Dumstrang so their history of magic I presume would have mentioned briefly about Grindelwald, the dark lord in their part of the world.) And eventually the truth about his connection with Grindelwald would surface soon. But of course, no one will know it, except himself.