As I was wasting time, waiting for the arena to turn up, a thought struck me. Notice how on the gate map, the Core has that white checkered pattern? Does anyone else recognize that aesthetic? Why, it's a spitting image of Sanctuary.
Is Sanctuary actually located somewhere in the Core, and as it turns out, the only way to get in is through Shadow Lairs or a direct invitation from whatever is inside it? It would explain how Alpha disappeared other than "I dunno, they must be in the Core because they aren't anywhere else" *and* explain why the knights at the terminal have no idea how to get in (seriously, go talk to them; they really have no idea other than a guess about minerals). Alpha could be reasoned to know about Shadow Lairs since they were a fighting team, but knowing how to open the Core? Not so likely.
I posit that Alpha were taken by the Swarm instead, and the only reason we aren't taken too at the end of a Lair is because the Core itself brings us into it. It would also explain why the alchemy machine is so powerful. It's wired directly into the heart of the world.
Or am I just crazy? Perhaps there's already a thread about this and no one cares? >_>
TL;DR:
Stop moaning about how the core hasn't been opened. It's been open for months.
If Sanctuary is the core then where are Alpha? Just gobbled up by the Sanctuary and dead to the world? Or is there a deeper level to it?