The Mursaat and the White Mantle
I wouldn't be surprised if somebody has already mentioned this, or if it was even explicitly stated in-game, but I think that it is a possibility that the Mursaat are 'training' the Mantle to become the new guardians of the Door of Komalie. Sure, it's a bit of a stretch, but it would fit with the oppurtunistic nature that I have observed in the Mursaat (they used Abaddon's own power to keep him sealed in at Hell's Precipice--I think it was Abaddon that created the full stone (before it was technically a Bloodstone, i.e. in one piece and not five) in the first place)--if they suddenly ended up with a major religious sect worshipping you as gods and following your orders and they're as oppurtunistic as I think they are, surely they'd start to not only use them as their 'conduit' to perform their will on the main part of the continent but also perhaps subtly train them to take over from them?
The only real evidence I have of this aside from the assumption that the Mursaat are oppurtunistic is an extract from one of the tablets of Janthir, but meh, I think it fits personally:
In a person's life he may encounter many doors. Some of them will be shut. Others will be open wide. But those with locks should remain shut tight, for faith comes in the acceptance that there are some things best left alone.
-- Verse 4, Book of the Piety
If you ask me, this is a pretty clear reference to the Door of Komalie--those with locks should remain shut tight? Certainly the case with the Door of Komalie.
P.S. Just in case anybody mentions that the Mursaat used the soul batteries to seal Abaddon in and not the Bloodstone in Abaddon's Mouth (which I think is the keystone, personally--it certainly fits with the different design and significance in sealing the Door of Komalie.), as far as I am aware the soul batteries served only to 'control' the power of the Abaddon's Mouth Bloodstone and use it to seal the door: the actual energy for the door's 'lock' came from the stone; the souls of the Chosen were used to maintain this lock and stop the door opening, as seen in Abaddon's Mouth when you destroy the batteries and the door opens.