Here's the only other thing you can really say on the subject:
Mass Effect Lead Writer
Drew Karpyshyn
Mass Effect 2 Lead Writers
Drew Karpyshyn & Mac Walters
Mass Effect 3 Lead Writer
Mac Walters
Also, keep in mind that the original Mass Effect 3 ending with the dark energy was Drew Karpyshyn's original idea from the start, hence the strong foreshadowing in Mass Effect 2. Because he left and the ending leaked, Mac Walters & Casey Hudson slapped together a new ending and called in Mark Meer & Jennifer Hale to do the voice acting. Keep in mind too that the catalyst's voice is a combination of both Meer & Hale; that's why in the shipped ending there is no other dialogue with any other characters.
Other than that, nobody knew. Another writer, Patrick Weekes, even slammed BioWare regarding the endings over twitter, but the tweet was removed and he had to issue an "apology". You can still find the tweet all over the internet though through google searches.