Here's what I've gathered as fact
The eye of the mealstrom is a one way portal to the Cothica and if it closes then in Peytons words "the mugic of all tribes starts playing out of key"
We can also confirm that almost everyone believes it was in the hands of one of the tribes at one point though no one player or creature can agree which tribe it was.
And despite never actually seeing it it somehow holds enough sway to keep the tribes bitter rivals (though that dosen't take a hell of a lot).
These 3 things are all I am willing to state as fact about the Cothica, now for a bit of speculative grounds,
Heptadd and Narfall have both been believed by other creatures where the Cothica is (Heptadd even believed to have tapped into it) Now we know at the end of the series that Heptadd is a spirit lander so in theory unless we open up a very possible debate as to whether the spirit landers have any ties to the Cothica this is a no go.
There is also a variation of Mudeenu that has a quote on it about believing the Mipedians have found the cothica and how Mudeenus new power makes that very believable, though this is only one variation on a card that is from a time period we never saw in other media so this is also an unconfirmed setting.
So that's what I can gather, now my belief for the Cothica is that it is an other worldly place that is in fact connected to the spirit landers (remember Mugics are cast by channeling the spirits of ancient mugicians... Note spirit in that statement) and is an entity that was never actually on Perim but was perhaps once more noticeable in Perim but the power dimmed which is why they now have to give up mugics at the eye of the mealstrom (because the connection between the Cothica and Perim is slowly closing)
So there's my rather long conversation starter, where we go from here is anyones guess, any takers? `