I don't often post here (understatement),
but this time perhaps I should. The IT was afaik not in any way shot in the foot or proven 'wrong'.
It or IT simply has not been confirmed as 'the' or 'a' possibility thusfar.
And why would they even do that?.. "Oh yea hey the IT is true by the way" *major ending DLC spoiler.
What?!
For real?..
Anyone expecting bioware or any other official source to make a statement such as that? They will not spoil nor admit any possible endings. Of that I am certain.
I'd wager they want people to 'see it unfold for themselves' and yes there may be multiple possibilities in how the "Extended Cut" pans out.
Another thing some people might want to concider is that bioware has been trying to play us for fools before. Not so much in a bad sense. But provoking response and making people talk about the game trough various means.
I remember well the Mass Effect 2 teaser showing sheppard armor and a Geth at the end of it.
(Loved the theories floating around about shepard being turned into a Geth and what not, had some laughs there)
Or the deal with "Sheppards death" in the 2nd installment.
I am pretty convinced Bioware has intentionally poked us for responses on manier an occasion.
The last one being ME3's, by now, (in)famous ending.
I think I've already made it obvious that I do believe in the Indoctrination Theory still and here's some of my reasons for doing so. Things I believe 'might' be possible or true.
1) The IT is either truth, a possible truth (path) or perhaps a partial truth.
There's just too much pointing in it's direction to just wave it away.
[on that topic the video about the IT on youtube is a 'must watch' if you want to understand where it is coming from and want to succesfully argue against it. You may find yourself challenged for the latter to say the least.]
2) There have been no suggestions afaik *whatsoever* stating that the "IT" may be or not be true.
All I've seen thusfar, are statements which have neither confirmed the possibility nor denied it.
3) "They're not going to change the endings, they are going to *expand upon them*"
You do realise this speaks very very very much in favor of the IT as is.... If you do not, I think you may have missed it's point.
4) Expanding up on the endings; Clarifying the current excisting endings;
Sounds to me like there is extra gameplay planned currently along with cinematics explaning the current endings. Giving them more context and eventually leading us to...*insert still open possibilities here*
I actually believe our current "ending/endings" could be classified as being a 'cliffhanger'
and that the EC DLC may expand upon what happened there as well as the consequences of the choices you made there and/or troughout the entire game itself.
5) While in many ways questionable.., I also believe this was 'sort of' planned by Bioware's mass effect team. I believe the main draft for the game's extended ending already excisted long before the Mass Effect 3 was shipped and shelved.
Sure they are listening to feedback now and very likely making changes/additions to the full extend of it so that it is as gratisfying and gives as much closure for every possible thing of imprtenance out there. For all the *bizillion* choices you could have possibly done different so to speak.
The feedback would be helpful in such a way to make certain nothing is left forgotten or unconcidered and the full ending is to become an as memorable as possible conclusion for as many as possible of the playerbase.
That is my 2 cents on the matter ofcourse.
Commence calling me a fool after we've all been proven wrong and the DLC ends up putting in a *yellow option* instead.

But not as long as there has been nothing noteworthy to prove it 'untrue'
Regardless, thanks for braving my TL;DR
On a last note;
"I love the current endings as I am comvinced that they fit into a greater whole. One we have yet to witness."