I like the idea of Primal/alternate forms and Regional Forms, and I think, beyond just giving more pokemon new typings, it allows people to think of pokemon in a different way. For example, if you think a pokemon fits the typing it has right now, but also think it has reason to be a certain type, you could say that it should get a regional form with that typing, or an alternate form if it fits more. For example, if both noble and hero were to be added, the swords of justice, who all make sense as noble, hero, and the unique typing each one has, we could make their noble forms their original forms, and give them a regional form (or resolute forms, to make it fit with Resolute Keldeo), which replaces their noble-typing with a hero-typing, or vice versa. overall, I think that using these will help us with adding new mons with those typings, while also not resorting to fakemon.
as for how powerful the primal forms are, I don't think i'd be able to tell without using them.