Is it correct to consider the Heart of Lorkhan a unique Crystalized "Gem" (Not related to the Soul Cairn) capable of containing (and releasing - through a specific channel) the Essence of Lorkhan (and Mundus) and also absorb souls from creatures, sentient or not, which are inside or bound to that same Mundus?
Since souls are used to recharge magical devices, souls are connected to Magicka, pure and simple. Magicka is Power inside Mundus. It changes the shape of things, be it on natural or supernatural levels. So, by this reason, who controls the Heart, controls the Anchor of Mundus.
Is it a valid theory or this conjecture is something that doesn't make sense according to the valid references?
It makes sense to me. Although the Soul Carin is full of souls from used soul gems. Not specifically channels of magick into the Mundus.
First: The Heart has no relation to soul gems or the Soul Cairn, but that doesn't mean that there arn't any simularities.
Second: The Heart is controled by no one, though some have found a way to minipulate it.
Third: The Heart does not absorb souls, it posseses them.
Could you site any in-game books that support those statements?
I wonder if Lorkhan's Heart was in any way related to the Star of Azura-- assuming that it had soulgem-like properties.