As for north american natives, most weren't organized enough to deserve a country, they already are pretty well-represented with the current native system in EUIII, the more organized native americans were in meso or south america.
Arguably true on the first part, bollocks on the second. The in-game native system is an abomination that's utterly divorced from anything remotely related to XVI-XVIIIth century history, where the natives were important players in their own rights, not simply random disconnected villagers who got slaughtered when white men walked into their territory. There is not a shred of "good representation" in that system - it's wrong from start to finish.
First off, of course, in a lot of cases initial relations between natives and settlers were relatively peaceful. The game is very poor at handling that, because itS' all up to the RNG and an arbitrary aggressivity number whether you have good or bad relations with the natives.
Second off, natives and settlers in several cases formed alliances (The Iroquois with everyone who wasn't French, and the French with everyone who wasn't Iroquois). This cannot happen in the present system at all.
Third off, the "Natives uprising" within already settled territory often occured decades after settlement (Powhatan war, 39 years after the founding of Jamestown; King Philip's War, 30-50 years after most of New England had been foundedm, etc). The system doesn't allow that, because the second a colony has 1000 settlers it automatically become a city and the natives vanish.
Fourth, native uprising were not one province affairs that ended as soon as they began. Father Rale's War was fought form Nova Scotia to vermont. King Philip's, from Connecticut to New Hampshire. And that's some of the smaller ones. The Cherokee/Chickamauga wars, the wars for the old northwest, etc were fought against far broader coalitions of natives over a far broader territory. They also often involved the natives leaving their territory to attack points on the other side's territory.
Fifth, while they were disorganized by the standards of other nations and governments, and while support of the overall group was often handled on a village by village basis, each village deciding whether or not it would join the general effort, there WAS a greater sense of unity to many of these groups (and the Iroquois especially so). They were more in the nature of extremely decentralized confederations, often without formal leadership, than in the nature of villages that had nothing to do with each other (your so-called "well-represented")
Nomad natives in the americas really screwed colonization for the AI tough...
That, on the other hand, is the plain truth. I wrote the mod for it, and came to the very swift conclusion that it just didn't work. Any colony got turned to ashes within weeks of being built, and since once the colony was conquered there was no longer adjacency between the horde and the colonizer, it resulted in an automated truce.
My next plan up will involve regular old countries. It will also include fewer natives than the original mods - the focus will be on those nations of the Appalachian-Great Lakes region, the ones that fought the Beaver Wars and Old Northwest Wars in the north, and the Civilized Tribes in the south.