Nikoka said:
I think Nanika may be a Gas-Lifeform or it's related to them in some way.
http://puu.sh/94Ygw/6ec9ac8ce5.jpg
Pay attention to the panel with with squashed up body parts.
http://puu.sh/94Y7P/93cfa6e007.jpg
What happens when someone refuses 3 of Alluka's requests. Looks incredibly similar to what we see in the lab does it not?
http://puu.sh/94YvV/40d8f7b08e.jpg
The Gas-Lifeforms appear to be capable of speech, we only see one of them saying the word "Ai". It is also the word Alluka says when she grants a wish (notice the あい kanji in both panels), it was translated as "Aye" or "Okay" by the people who translated the chapters in english.
http://i32.mangareader.net/hunter-x-hunter/321/hunter-x-hunter-2734775.jpg
Silva insisting that he doesn't consider Alluka family.
http://i24.mangareader.net/hunter-x-hunter/321/hunter-x-hunter-2734777.jpg
Were the Zoldycks part of an earlier expedition and brought Alluka back from the Dark Continent? "It is something that came from a different place. Something dark." Sounds like the Dark Continent to me.
Interesting observations. As I compare for myself maybe Silva wasn't referring to Alluka per se but her ability, Nanika. This is just speculation here but maybe like that hunter contracted immortality (which as far as diseases go is...interesting) maybe somehow Alluka contracted that Nen ability? Maybe they were part of an earlier expedition. Maybe when Alluka wasn't born and still a fetus inside Kikyo and something affected her child. A whole lot of possible things but the Zoldycks seem to be connected to this continent, So Killua could pop up again and more characterization for Alluka hopefully. Also still speculation but that gender confusion with Alluka thing might be more plot related than Togashi being an ambiguous tease.
And I'm gonna go out and say this will be darker than Chimera Ant arc.