Well, for starters, there's the question of why we wouldn't bring some Reapers with us in Control and especially in Synthesis, especially when they'd be our most viable form of travel.
Further more, regarding Sythesis completely we're all cyborgs now, and the ending slides really drive home the point of us becoming really goddamned advanced because of it. And yet that conflict that is going to happen is going to have the same level of difficulty for the Synthesized society as it would for the others, even without Reaper back up? The characters are going to behave in exactly the same way despite being cyborgs in one playthrough and not in the other? Because if not then what the hell was the point?
Even with the Changes happening change wont be instant, the Synthesis ending mostly talks about the future EDI hopes they will achieve, eventualy. They might have gotten hold of some Reaper Tech and knowledge, but they havn't got any post Singularity Tech until they start creatign it. In a way, they have been enabled for further development change and Tech development, but it's still their job to accomplish it and work for it.
The Geth were AI but they hadn't advanced beyond the Reapers, still they had advanced Tech, no doubt about it and they favoured the most high Tech solutions.
Technological evolution is not a miracle that just happens, it's born out of need for something and hard work.
Think of Shepard as the Blueprint for the change, how much did Shepard change? Synthesis might be slighlty more but from what commes through, Shepard provides the designs, which commes from the Lazarus Project, using a combination of Cerberus and Reaper Tech to upgrade and change Shepard.
How strange was Shepards behaviour in ME2 and 3 compared to Before that point? How strange was Shepards Cyborgness?
Seeing the Pictures, I would expect them to behave fairly similarly. They still come together in classrooms, they still spend time together they still work. They still reach for different goals. But they might have an easier access to knowledge which could affect the speed they process a problem or find answers or analyse scanner data.
Also, I don't expect Bioware to make Three different versions of ME:A. They either launch Before ME3, or they pick an ending and I don't Think Synthesis would make things woulse, in fact, it could explain new cool abilities of the main character and companions and fighting techniques.
More interesting moves and combos.
I tend to favor Control, even if it's questionable to enslave the Reapers who are already voctims, but it saves the Citadel and it allows peopel to make choices about their future and saves the Geth aswell.
Synthesis, is ok, imo, but the exploding Citadel with all those millions of people on it, is kind of dissconcerting... Some tweets claims most of them were safe in sheleters though..
But, I expect them to go for a pre ME3 ending launch. Ignore the ME3 endigns all together, run an Andromeda Trilogy for a decade, then possibly continue on that or go back to the Milkyway when most people have forgotten abotu the ME3 endings or matured to the point where they don't care enough to make too much of a fuss about it.
We can probably continue the ME3 ending discussion after 2025, if they announce a return to the milkyway. Somehow I doubt it unless Andromeda is a failure. They wern't happy about how spread out civilisation was in the milkyway. Even if it was said that only 1% was explored, it still looked like civilisation was all over.
As for the Reapers, In synthesis, they have free will, and they help the people of the milkyway as a form of redemption. They are not a form of transportation but sentient beings. (I guess they could provide people passage ifthey wanted to though)
In Control, they have been Conscripted by the Shepard AI, both to protect, aswell as a penance for their crimes. They are paying back by rebuilding and helping to protect people.(least in the Paragon endings)
Renegade endings could be more dictatorial, but not that very hands on.
I doubt the Reapers would follow in either of those endings, unless there was a Reaper in Synthesis interested in exploration. If one of them followed, then it might have been destroyed in the initial attack trying to protect the colonists from the hostile natives.