You see, once Clint saves Wanda from the thief and he faints upon seeing her, she takes him home, and she tells him that they can't wake up her Aunt Agatha. This is when we first see the door, the door to Aunt Agatha's room, not a closet, but I guess enough people have figured that it was a closet that it is now most commonly referred to as a closet instead of being another room.
Clint, naturally, is all "Ummm..you don't have an Aunt Agatha. You have an old witch friend named Agatha that talked to even after she was dead, but that's it."
But that doesn't keep him from sleeping with Wanda...
Afterwards, he can't help but look to see who the heck is in Aunt Agatha's room....
So yeah, what the heck was in Aunt Agatha's room? Eventually, Doctor Doom shows up and takes Wanda from Transia and leaves a Doom-Bot in her place (I joke about Hawkeye sleeping with a Doom-Bot, but the odds are that Doctor Doom removed Wanda AFTER this encounter with Hawkeye - but we don't know for sure, which is sort of an unresolved story in and of itself).
Since we've all moved on from this, it is unlikely that we'll ever know what was in that room. But maybe someday!
Ron Richards of iFanboy repeatedly asked Bendis about it, leading to this amusing exchange during their Age of Ultron discussion:
Finally, I asked Bendis if this story would tie into and resolve the dangling plot line of the Scarlet Witch/Hawkeye/Closet story from The New Avengers #26, of which Bendis responded with laughter, “You are an insane person. No matter what we’re talking about, you bring up that *expletive* closet. We were talking about the All-New X-Men and you brought up the closet. You are nuts. I love that about you. This is fantastic.” And then he dismissed the question by saying that behind the closet door was Ultron and laughed.
That's how ingrained the "closet" angle is! Bendis himself even refers to it as a closet!
That's it for this installment! Thanks for the suggestion, Jason! If anyone else has a suggestion for an interesting unresolved comic book story, drop me a line at firstname.lastname@example.org!