The controversy over Mass Effect 3's ending has come and gone, and BioWare has learned a few valuable lessons. Still, it's hard not to wonder what would have happened if former lead writer Drew Karpyshyn had seen his ideas through to the end, and luckily he's shared those details.
Karpyshyn told the radio show VGS (via Eurogamer) that he originally planned to do more with the idea of Dark Energy. The plot element was mentioned a few times in ME2, but fell by the wayside when Karpyshyn left near the end of that game's development.
Though he said the plot "wasn't super fleshed out," the Dark Energy was meant to be accessible only by organics. He suggested that the characters may have learned that using the Dark Energy was disrupting the space-time continuum, and the Reapers may have seen that as their motivation to wipe out life.
"Maybe the Reapers are looking at a way to stop this," he said. "Maybe there's an inevitable descent into the opposite of the Big Bang (the Big Crunch) and the Reapers realize that the only way they can stop it is by using biotics, but since they can't use biotics they have to keep rebuilding society--as they try and find the perfect group to use biotics for this purpose. The asari were close but they weren't quite right, the Protheans were close as well.
Karpyshyn also noted that his own ending might have upset fans just as much as the real one. Two ideas floated under him were Shepard unwittingly being an alien, or Shepard transferring his essence into a cyborg to become "a bridge between synthetics and organics," similar to the actual ending. "Some of the ideas were a little bit wacky and a little bit crazy," he said.