My theory on the new Turtle: It's a regular Pokemon and Terapagos is a Paradox counterpart, or an inverse relationship where one is derived from the other ala Silvally and Arceus (maybe Terapagos is the original and this new Turtle is the "imaginary" nature of Paradoxes to mass produce one instead).
My only grounds for this being that the Kubfu/Cosmog/Calyrex mechanics were basically a way to enforce Version exclusives, which I'm not sure I see them doing since so far Terapagos is the only mon of this nature/resemblance we've seen, and it was a "full-evo" type of look. It also seems like it's meant to be an "all-types" gimmick mon, which removes the sort of Type + Playstyle difference Urshifu and Calyrex forms had as factors as well on the same mon (Solgaleo/Lunala being two separate big box-art mons rather than different Formes of the same species)
My only grounds for this being that the Kubfu/Cosmog/Calyrex mechanics were basically a way to enforce Version exclusives, which I'm not sure I see them doing since so far Terapagos is the only mon of this nature/resemblance we've seen, and it was a "full-evo" type of look. It also seems like it's meant to be an "all-types" gimmick mon, which removes the sort of Type + Playstyle difference Urshifu and Calyrex forms had as factors as well on the same mon (Solgaleo/Lunala being two separate big box-art mons rather than different Formes of the same species)