So far, Skull Warriors were the worst villians in both Generations. You want to know why? They had no backstory, no motivation, and practicaly no personality.
They were just zombies the Heroes had to kill to get the Mcguffin.
The only way I would ever see them added to G3 was somewhere way past the 3 year plan, maybe as a faction of fallen warriors that were raised by something and want to take over the island because of it's growing corruption. Maybe they'd see it as destroyed culturaly and would attempt to restore back the glory days they lived in by conquering the island and transmforming the society into a better place.
As to who raised them, no idea. Makuta would be defeated, Karzahni probably used for another plot point and we have no mask that is capable of raising the dead yet.
Still, I don't see it happening, there are many way better villains G3 could adapt.