Ok, I've been wondering if there's a reason why the files refer to the orb as Mythal's while she refers to it as Solas' and have been coming up with various theories (such as it being a gift, or that it belonged to her before she died and he took it after) but this is my favorite one yet.
We know the Gods in the pantheon are something special. Likely not mages or spirits but something else.
We know from the legends that normal elves can become gods.
A common theory about Fen'harel is that he was no god to begin with, like Ghilan'nain.
What if *checks tinfoil* the orb is... Godhood. An artifact made to bestow divinity to regular people. Solas was too weak to unlock it after his slumber, denying him his godly powers. Sackspla-- I mean Coryflor--(he has too many great names) sought to become one with it.
One could argue that the Inquisitor is reaching demi-godhood with the mark towards the end...
Headcannon: The orb's power is turning Lavellan (and all other inquisitors...) into a Goddess! I'm of to make fanfiction and fanart about it! *runs off squeeling*