The new race could be something like Darth Vader, General Grevious, or the Adeptus Mechanicus Techmarines, in that the race was once of organic form but have simply replaced their limbs with robotic parts.

This satisfies the echo portion by having the beings originate in organic form, but have chosen on whole as a race to "better themselves" physically with robotic appendages.

There could be a light and dark version of the race. The Light version has qualities and a personality and looks more human than robot (unexposed metal parts, acts human, etc), whereas the Dark version care not for projecting a human image (terse personalities, may have gapping metal parts sticking out of body, tears in the flesh covering body, jaw missing, red lightbulb in eye socket, etc)

Though the example I put above sounds a lot like the beginnings of some Necron-like Terminator horror plot line for the game. I would assume the developers could weave the race into the game like the Domans; refugees that simply integrate/have been hiding amongst everyone this whole time.