The "Into the heart" prophecy (see section 4.5) suggested that maybe somebody besides Rand would remove Callandor from the Stone: "Who draws it out shall follow after". In TPOD this did happen, although not in a very dramatic fashion. Narishma went to Tear to retrieve the Sword That Ain't for Rand. Bo-ring. Fortunately for our active imaginations, we still have lots of fodder for Callandor theories.

What's the deal with the "flaw"?

In [TPOD: 27, The Bargain, 539-540], Cadsuane tells Rand about a flaw in Callandor, which she claims to have discovered in some moldy documents in the Tower Library:

"It is flawed, lacking the buffer that makes other sa'angreal safe to use. And it apparently magnifies the taint, inducing wildness of the mind. So long as a man is using it, anyway. The only safe way for you to use The Sword That Is Not a Sword, the only way to use it without the risk of killing yourself, or trying to do the Light alone knows what insanity, is linked with two women, and one of them guiding the flows."

This not only explains the mess Rand made of things at the end of the Ebou Dar campaign (which was compounded by the Ebou Dar Power Anomaly), but also the megalomania displayed by Rand during and after the attack in the Stone in [TSR: 10, The Stone Stands, 136-138]. What insanity? As John Rowat points out, "He went a little nutso, thought he could raise the dead, and it took him an hour or so to realize that he could just fry all the bad guys at once." Also, it explains a statement by Siuan Sanche in [TDR: 29, A Trap to Spring, 276] in which she refers to a woman wielding Callandor. In particular, she's talking to Ny, and says, "With Callandor in your hands, child, you could level a city at one blow." Previously, that seemed really silly, since Callandor was, as far as we knew, a male-only sa'angreal. However, Cadsuane's statement indicates that Callandor can at least be used by a circle of two women and one man, with a woman controlling the flows (and thus, effectively, wielding the Sword That Ain't). Given that Siuan has made the Dragon Reborn her life's work, it is reasonable to suppose that she may have discovered and read the same moldy documents as Cadsuane.

Now we must ask, why was the thing flawed in the first place? John Novak gives us some ideas:

"Given that it was made in the shape of a sword and seems to have no other real purpose than as a weapon, I think it is safe to say that it was created either during or after the War of Power. In either of these cases, it was probably the result of one serious-assed QRC (Quick Response Contract). That alone will increase the probability that things aren't exactly up to specifications. Further, if it was made after the war, then by definition it was made after the Taint was created by the Dark One. I would hazard a guess that men are needed to make a male-oriented angreal or sa'angreal, so there's another potential reason for it to be screwed up. Hell, for all we know, that was the last attempt ever made at creating a male (sa')angreal."

Who will use Callandor?

Looks like Jahar Narishma gets the honors for that one as well. He uses Callandor during the Cleansing in the final chapter of WH. So it appears that he "follows after" as well as "draws it out".

This may well be the fulfillment of Egwene's dream of a dark young man holding something glowing in [ACOS: 10, Unseen Eyes, 203], though the vague wording means we can't be certain.

What does "The three shall be one" mean?

In Min's studies of the Prophecies of the Dragon [TGS 48: Reading the Commentary], she finds the line "He shall hold a blade of light in his hands, and the three shall be one."   A likely candidate for the "blade of light" seems to be Callandor itself, which glows while in use.  So what does the rest of it mean?

The Commentaries on the Dragon speculate that the three becoming one refers to the three countries under the direct rule of the Dragon (Cairhien, Tear, Illian), but Min dismisses this as weaksauce. There are other countries that follow Rand and more probably to come before the Last Battle.

Fan speculation has centered around the idea that Callandor is only safe to wield in a circle of two women and one man. Cadsuane theorizes that Rand will link with two women and be able to use Callandor that way.  But who? Rand doesn't exactly suffer from a lack of choice with regard to female channelers who would be willing to help him and would be potentially strong enough to handle that much of the Power. Let's run down the likeliest candidates:

Nynaeve: We know Rand trusts her and she has experience in mixed circles channeling massive amounts of the Power from the event at Shadar Logoth. She seems the most likely of any female character to join Rand in this.

Egwene: She's strong enough, to be sure. But with her and Rand on the outs right now, it's unlikely that he'd be able to bring himself to trust her enough to bring her into this circle. It's also unlikely she trusts him enough to accept an invitation, considering that she thinks he's a looney right now.

Moiraine: Possibly strong enough, as she is one of the stronger Aes Sedai that aren't one of the Super Girls. And we know she'll have some sort of role to play in the Last Battle, otherwise it wouldn't make sense to go haring off after her before then.

Cadsuane: Cads seems to know the most about Callandor. She was after all, the one who revealed to Rand the flaw that makes it dangerous in the first place. But after her failure to keep the male a'dam locked away from Semirhage, Rand has exiled her and threatened to kill her if she sees him again. After her continued meddling in the Stone of Tear, it seems very unlikely that Rand will be able to trust her enough to include her in a circle.

Elayne: As one of Rand's three lovers, she's definitely got his trust. However, with her pregnancy impairing her ability to channel reliably, it seems unlikely that she could be included in such a circle.

Aviendha: Avi is strong enough, and has Rand's trust. But one wonders if she can overcome her aversion to swords enough to handle a sword shaped object of the Power?

Alivia: The freed damane is the strongest Lightfriend female channeler. And her experience with offensive weaves could be invaluable if Callandor is to be used in a combat situation.  But would Nynaeve and Min allow her to get that close to Rand? Probably not.

Alanna:  If Rand's mood improves after his mountain climbing expedition in TGS, could he find it in himself to forgive her for bonding him against his will? If so, his bond with her might become an asset, rather than a liability. It's uncertain if she has the requisite strength to be able to handle a sa'angreal of that magnitude, however.