Already posted this but think it drowned in a post storm some pages away:
Illusions usually let the mind do the work for them and let it decieve itself. This would explain why the confrontation with TIM plays out very similar as the one with Saren as Shepard thinks both had initially good intentions but got indoctrinated (if the dream starts before entering the citadel).
Andersons death then perhaps is a symbol for S. Believing for them to be to late.

Shepards own mind doing the main work also gives us an explanation on why the War Assets influence the endings. I think it would go like this:
The more readiness you have the higher Shepards determination and willpower are and changes the outcome Shepards deems possible.
On the different kinds of endings i think it's true that destruction frees him and control enslaves him but sythesis needs a much to high amount of war assets to be a bad outcome for him. It seems more like a back door his mind wants to show him, another way he could go to defeat the reapers.
(actually changed my mind on this part. I think new options are added the moment Shepards willpower (war assets) reaches a level where the cearlier choices won't work as intended anymore. so on low assets even with choosing destruction he would loose the mindbattle but reaching higher levels changes this. The same with control and perhaps even with synthesis.)

reason why he isn't shown alive afterwards: it would give away that it's not real too easily.
And he dies in all of the possibilities because he himself doubts that he will survive this.

Read about this theory of yours yesterday and afterwards i remembered some things:
- In an interview i stumbled upon it was hinted at by bioware staff that the playtime is about 50% more then ME 2 now that would get me to about 60h but ME3 capped out at around 30h.
- There was a lot of talk about wrong leads and us hunting for differen solutions when there is only one
So perhaps we not only didn't see the real ending but we still get half of the game at a later time and this waiting is a part of the experience. Except while on PC that wouldn't be much of a problem with Origin being needed to actually play the game (perhaps also a reason it's mandatory),
how would they do it on the 360? On the PS3 it could already be on disc, the space is there and there either is a timestamp which unlocks the content or you need a patch to do so...

Edit: Oh and don't know it's already said but after you return from entering the Geth server EDI says something along the lines of "how do you know you are in reality now?". If this theory is true it would make this statement one hell of a foreshadowing.