The problem with Synthesis is coming up with an interesting story when everyone and everything is interconnected and the future is all lovey-dovey cyborg unicorns puking techno-rainbows.
Plus the post-Synthesis universe falls apart as soon as anyone puts any scrutiny into it. If it was written by a pro-Synthesis writer the world building would be an endless chain of papering over the massive cracks of logic. And an anti-Synthesis writer would turn it into a horrible dystopian anti-ME3 hate-fic. Neither sounds that fun.