I wonder if it evolves from carbink
how much you want to bet it's going to be like mewtwo. Ditto was failed attempts to create mew, and mewtwo was the closest they got but it went wrong.
carbink is a plebby carbonite creature, but diancie is compressed carbon in the form of pink diamonds. They're related and there's no doubt, but I highly doubt they're going to evolve into one another.
there's been a lot of normal pokemon related to legendaries so I don't see why carbink can be an exception.