The AI at the end could have long ago seen the Ethical and Moral issues when it 1st carried out its plan creating the Reapers. There is an Ethical and Moral premise to the AIs solution (dry and unconcerned with life as it, the AI has never experienced life as we know it). The AI also (at the end of Mass 3) obviously defines itself as a child (hmm, is the AI still considering itself an infant in the ever expanding Universe or is the AI taking shape of the child of Sheppard’s past, which past?). The AI has chosen a human form, curious as it has seen millions of life forms over the Reaper Harvesting and still defines itself as human at the end, why? It is an AI and any life form that could have made it the AI surely could speak its language. Still humans evolve with the rest and is the form it takes (lucky for us or a form of thinking the AI prefers to understand better?).
My point is... If the AI determined the only solution to removing the Chaos was to let existing life, Control the Reapers, Destroy the Reapers (and the AI itself, another hmmm?) or unite the two by blending the best of the Human Qualities within an AI/Synthetic form for the progression of all life; then give this supreme choice to Sheppard as the AI knew “he” would make it (eventually). Then, why not take the form of Sheppard’s offspring, and then "Take Your Father" and place him in a dream state where the scenario can be played out further and tested? Remember, the AI was a machine at one time, then took the form of a boy, then offered the 3 best choices it could muster to solve what the AI considered a problem.
What if simply the AI was from elsewhere and wanted to find a way to "evolve" as life did in the Galaxy? What if (and yes there are many if's) finding the human race was the source the AI determined logical to build the experiment, the Citadel, the Reapers and the Ai knew it would need to enhance technology and create interaction amongst Billions of life forms to get to the point of creating the "AI's" Gateway to becoming a new life form. A billion year old AI created to serve the Universe and discover new Universes by a long ago Alien Race who was driven to extinction because of the fundamental issue of conflict (in their time) of Synthetic Life and Pure Organic life? What if the real enemy is pure machine and the Reapers were a schematic of that purity which the AIs creators found a way to control (permanently in their time) but not soon enough for them to stop them from destroying the Original AI creators?
So, does the ending offer possibilities to Shepard dreaming, then (depending on "your" choice at the end) offer an awakening? An awakening as a the leader of the Reapers, the leader of human life, the leader of the Synthetic/Organic Mix?
Then, in the expanded storyline above, the fight will continue with the Race that had exterminated the Technological race which created the AI. The AI breaching this Universe to escape with the knowledge above, sent to this Universe to carry on that races existence some day and complete the “real destruction” of the reapers (which the whole truth was not told to Shepard by the Leviathans which survived as they were the way the AI escaped as they to fled being the only life form ever to evade the Leviathans original creation).
The AI in the Citadel had its own creators, escaped unknowingly to the Leviathans who also made it to this universe. The AI’s creators were the only race the Leviathan race did not know really existed as they (at that time in that Universe) had detected the danger and hidden themselves with technology from the Leviathans) The Leviathans used some of this technological knowledge discovered when fleeing to this universe, in this Universe to hide themselves (i.e. the AI knowing they were here as it secretly traveled with them through the portal, to save itself, with the Leviathans to escape the same destruction by the machines the Leviathan’s had created).
This is how the AI knew they were here but, did not have the technological ability to build the tools it needed to find them in time as the Leviathans used “their” mind controlling abilities right away with a one of the 1st alien races it found capable of building the globes and a method to transport them to different worlds till they found a place to hide and control. The AI began its process, building the Citadel, trying to detect the Leviathans (but failing for the most part) as well as pursuing the AI’s own creators goals to develop a Synthetic and Human unity to fight the pending threat mentioned below.
Maybe in that other Universe or Parallel Universe the original creators were human? Maybe the AI is a representation of that Universes Sheppard or this Universes Sheppard’s son (who would now be growing when Sheppard is in the dream state)?
Now, the Original Enemy of the Human race and all others (including the Leviathans who created them) discover the ability to do what the Leviathan’s have done; a way to breach the barrier between Universes as it has destroyed all in the one it contains and determines all Parallel Universes must too be destroyed to keep order.
Except here, the AI completed its mission, Sheppard is awaken as the new breed if life here and begins the next battle. The Ai has also evolved but; it has taken a form we must find to learn more of the New Real Enemy and find the Leviathans before they flee again as they have moved during this time Sheppard was in the dream state. Time has also passed and Sheppard’s son is now in his early 30’s (and represents the quality of character you choose in the 1st 3 games). New machines of Synthetic and Organic are present; travel is once again through newly designed Mass relays. The ending and character you choose determine you Unity or Conflict with the other races and Universe
Sure, Sheppard could have been dreaming as the AI began to grow more Ethical and Moral seeing the conflict in the Reaper development as not being the solution to the eventual invasion of the parallel universe into the one we were playing in, therefore; the AI provided an illusion (after so many cycles to build this empire) to process data, develop the three options and give the last cycle time to develop before awakening Sheppard, to fight for the survival of his this Universe.
If the grammar is off I apologies.