This is not correct. The earliest leaked versions of the ending have Shepard surviving in high-EMS Destroy too. That's in the version where the kid is still known as the GUARDIAN and none of his dialogue was written yet. Synthesis was about becoming "one with the Reapers," whatever that means.
(I guess there's still time for me to engage in ME3 design history pedantry.)
Well I heared before release of ME 3 that they had to change entire ending along with parts of storyline which inclueeded not some Star Kid only Dark Matter - you know this topic which Tali was investigating on her mission for Quarians back at ME 2.
Then someone leaked thing about this and yep. BioWare make Star Child.
I may say that Extended Cut did fix few terrible thing in ending, but still I can't tell HOW Shepard was supposed to survive blowing up of this Citadel Central - you clearly see it explode, and Shepard is RIGHT OVER THERE since it was she/he who blowed up the damn thing.
Entire ending is like "Well, kids it is all because of SPACE MAGIC you know ?"
How she survived this blow, and if she survived then how she survived being thrown out back to space ? Or how she did end up on Earth (I guess) at the end where you can see her/him breathing under some rubble. It does seems to me like Earth.
So how was this meeting ? Shepard came into this teleport and what ? Did it teleported her only by mind ? Like .. telepathy ?
Did she was having this entire discussion inside her brain ? And in the meanwhile her body stayed phisically back there on Earth and got hitted by some force from explosion when she decided to blow up Reapers ?
That would have explained her body being with armor under rubble on Earth, because if my memory of this traumatic ending are correct she had NO armor back when she charging to shoot up that thing for Destruction ending. She was in uniform only.
That doesn't work good however when you try to do Control ending or Synthesis since it does require her body to be up there.
Unless Synthesis and Control are means of indoctrination - which as we know BioWare does not like as theory.
I have like millions questions to Mass Effect in general with no answers to it for years.
Oh Synthesis ending. That one was tricky, it was to merge Shepard DNA with everything to make it well all equal. No more synths versus organics because they won't be synths and organics only this hybrids of them. I am not sure how could this merging DNA have worked on Quarians and Turians however since you know ... they have different DNA. It some real utopian idea here.