Okay. We've all seen the pic of Tahu Nuva rising out of the Protodermis with two things behind him.
Here's what I'm guessing. The Bahrag, Toa, Krana, and EXOs all fell into the same poll right. If the Toa were upgraded to the Nuva. What's not to say the Krana were mutated along with the EXO.
Now I'm not saying that they will evolve into Krana Nuva or Bohrok Nuva...but what if the Krana the Toa collected are transformed by the Protodermis into one of two things...
1) Blend with the EXOs or absorb some of the Toa's power and become Shadow Toa
2) Evolve into those massive spider thinges
3) Die And Something New Comes Along
We know the pool of Protodermis created the Nuva. So why wouldn't somethign that is left behind also possibly evolve or change or DO SOMETHING!