My idea for that was to be 1 alien species that is at 3 different evolutionary stages, but are all existing in the same time frame. Not even the aliens know this, until the reader does, by the main character finding it out.

I could incorporate your idea into it and shift the concept a little, but again, it would slide in nicely to my overall idea.

Basically, the two main characters are somewhat consciously connected. When one of the characters gets taken by ET, she is killed, and her 'soul' floods into the alien systems, the alien systems being based off of our previous Golden Age thoughts...in other words working purely through electricity and magnetism...and consciousness.

By merging with them, she changes as much as the aliens change through her mergence. The leap of consciousness occurring, then discovered by the second main character.

Oh, and there are no humans in the story, though the two main characters are most like humans.