Both Pokemon are confirmed to be Dragons with a secondary type that hasn't been revealed.
Guilty Guardian wrote...
My guess would be:
Dark/Dragon
Light/Dragon
The main problem with adding a new type would be that it will cause disruption to the balance of the current metagame. That's why Nintendo avoided doing so for the last 2 generations.
If it turns out like your guess, I hope Light will not disrupt the balance and add strategic value as much as Steel did. Dark was only added because Psychic was overpowered. It didn't serve much other value besides that.