Again, not a location that's appeared in any Marvel book prior, so far as anyone can tell. The name certainly hints at something Spider-like, but most of the big Spider-Man environments and storylines have already been confirmed. With Dan Slott's Spider-Verse series still ongoing with an immortal villain hunting down alternate Spider-Men and Women across multiple dimensions Arachnia could very well be the location that all finally pays off, perhaps with the surviving spider-people (including a teenage girl who pilots a giant robot and Gwen Stacy as Spider-Woman) live side by side. Maybe it's something completely different. Who knows?