Find out in the next episode of Attack on Titan Z: Frieza defeated!
/dead
This guy.
At this rate, it'll take the same amount of actual time for Naruto to timeskip for Eren to get in that goddamn basement. Seriously. Several seasons are going to pass before they get there.
It'll be while before the author even goes back there. I'm assuming all the answers are there that's why he can't reveal it so early.
I don't think the author even remember the basement subplot.
Maybe he does, maybe he doesnt. Who knows.