Considering this topic has been beaten to death in another thread....
You guys do realize you can take Share the Burden edict, which increaes productivity by 10% across the board? Essentially, Synths are already well capable of producing +30% technology, +30% minerals, +30% energy, as well as +10% food and +10% unity. Synth evolution is, from a game balance perspective, already borderline overpowered, it has more raw bonuses than either Biological or Psionic, and when it comes to min/maxing, it cannot be beat.
The real issue with synthetic evolution is threefold.
1: Cyborgs are already, by far, the most overpowered T1 ascension trait, which makes the jump to Synths a much smaller one than it is for Psionics and Biologicals.
2: Synths are utterly flavorless and boring. There is nothing to discern one playable synth empire from another.
3: Synths can already be produced, and given leadership positions without ever going down the ascension path. Ascended synths have no advantage over normal synths.