The question which inspired me this topic was that of the origins of Molag Bal. The Lessons of Vivec http://www.uesp.net/wiki/Lore:36_Lessons_of_Vivec,_Sermon_28 that he was the Chief of the Dreughs, at a time where the Dreughs ruled the world. Furthermore, the Dreughs themselves are described as "Altmers of the sea" in the same Sermon, hinting at an Elven root. This Sermon also claims that Bal had a different shape then.

To me, it is strikingly reminiscent of the case of Malacath. Both are exuviae of their former selves, both patronize a cursed civilization of Meri origin, both are now Daedric Princes. Further, both might be considered nostalgic.
Indeed, the description made in the novels of the remembrance, within the Ashpit, of a garden that once was, as well as the attempts by some Orcs of the last Orsinium to reinstate a cult of Trinimac, both could be seen as symptoms that the late Trinimac might be struggling to reach restoration. And maybe the Dark Anchors thrown by Bal to Nirn weren't meant at dragging Nirn into Coldharbour, but might be rather meant to pull Molag Bal Back to the Nirn where he once belonged?

So here is my first question. Could Molag Bal be, as Malacath is, of Aedric origin?

From there, more questions arise. How can an Aedra become a Daedra? And is there a way back (and hence a hope for Trinimac, and whoever Bal was)?

I was without even a definitive answer to the first question, but I have started to look in lore for examples of Daedric-to-Aedric conversions. And I stumbled accross http://www.imperial-library.info/content/shade-perilous. It is the only case I can remember of a Daedra sacrificing herself. This commitment to Jaciel Morgen goes far beyond faithful fealty. I actually think Deyanira loved her Mistress. If this act by the fair Katrece was indeed motivated by love, then it could be considered as Maran. Another clue in this direction is that she stated that she perceived love in her sacrificer.
Besides, Deyanira is also the one who pleaded the cause of Seducers to Jaciel. Could she have done it because she felt a trace of love in them?

Here is where I am getting at, and I agree this is a fancy, maybe even a mad suggestion or hypothesis. The Seducers are a Lordless Clan... Could they actually be Lordless because their Lord isn't a Daedra anymore? Could their former Lord now be an Aedra? Could the Seducers actually be responsible, due to the vestigial love they carry, for Deyanira's commitment turning into Deyanira's love for Jaciel?
In other words... Could Mara be of Daedric origin? Could she be to Seducers what Bal is to Dreughs?
In some sense, this would correspond to what love can sometimes be : a change (Daedric) that leads to Birth/Creation (Aedric).

Is there something which makes sense in all this far-fetched reasoning?

The Dreugh held the mythic role the Altmer hold, in the last Kalpa. They are not mer. Molag Bal was their Auriel, quite ironical huh?

Unlike On Boethia's Summoning Day, I think the Daedra are the Aedra of the previous Kalpa, and that Sermon has always been why.

Interesting view... So since there are 16 Princes, and 8 Divines, we're currently in the third Kalpa (assuming conservation of the number of Divines)?

Hmm, I actually never thought of that before. Oooooooooohhhhhhh, Talos is supposed to be unique to this Kalpa right, I think I read that somwhere? Oh man this makes so much sense now.