Can I do this? Is this white? I was inspired by Smothering Tithe, but tried to fit it to the world of Envertol. Also, I realize this opens white up to mass land removal.

­Smothering Tithe? Eh, not really. I don't think white should be getting unemotional ramp, which is basically what this is

Noted, maybe gets plains equal to artifacts and enchantments opponents control?

White very rarely does ramp at all, though I guess it is the next color after green to get it. It usually gets ramp via catch-up mechanics, though. I don't know that either your current iteration or proposition are in-color.

Hmmm. White does get to mess with enchantments and artifacts. If this weas "instead of" rather than "as well as" I'd have no argument with it. (Uh, apart from it accidentally nuking itself.)

Personally, I think I'd let this go as a colour stretch. It affects everyone technically equally; and it's late-game enough that although it's a huge ramp it's probably not going to be environment-wreckingly-good.

Turning artifacts and enchantments into only lands is solidly green's wheelhouse

Ok maybe then:

Enchantments are artifacts in addition to their other types

Artifacts have ": Add "