Well, like I said, it's not something I figured would happen within the game's lifetime. At best, I suspect the 13th will be joined either with the Source or the First somehow. I don't see the point in restoring it unless there's a way to reverse being a voidsent, otherwise Cylva and Unukalhai are the only survivors and both are conveniently on the First.
Supposedly, a partial rejoining of the First was on the table at one point. I doubt it'd happen now for gameplay reasons, but Norvrandt had such a dwindling population if there were a way to teleport them to the Source it could've worked except for the issue of Black Rose.
The shards definitely aren't a cut apple, were that true then rejoinings and soul mergers wouldn't be possible. I believe Lauront said that Oda has already referred to the situation as being unnatural and nature tends to correct itself when it can, it just couldn't due to Hydaelyn.
Regardless, it's my headcanon. :P I posted it not thinking there was any evidence to back it up only for someone to say it's supposedly possible due to dialog from the Studium quests (that I haven't done). I mean, if we're not going to get an AU then, for me, it's the next best thing. I understand why it'd sit ill with others though, which is probably why it'll end up in the "come up with your own theory" pile short of the MSQ doing something to make it impossible. They already ruined my headcanon that Azem was the one who saved Emet from being sundered (without knowing the future).
