I'm worried this is too much less good than the "destroy three target permanents" scheme, and wondered about making it scalable somehow, but it feels right as is, and surely this would have to cost 6+ as a sorcery, so must be in the right ballpark.

You know, Tooth, Claw, and Tail and All Shall Smolder in My Wake are rather similar.

Yeah, definitely. I think it makes sense there's overlap in "destroy N permanents" (there's at least one other as well that eats a flying and non-flying creature and something else) since there's so many possibilities and it's something you're happy to have multiple times in a game. But I didn't want to overlap so much the card felt pointless :)

­Into the Earthen Maw. Huh. Also a group (sort of) of three. Way to notice the pattern.

As a side note, does it seem to anyone else like Wizards "tests out" new illustrators on the multiplayer products?

3 is probably where you want it. Having played the World of Warcraft TCG Instances, I can tell you that having the boss monster/archenemy constantly reset the board is super, super annoying. It makes you feel like you should stop playing the game, or just pack your deck full of direct damage. While 6+ casting cost sorcery is probably a good guideline for powerlevel for schemes, if it's a global effect it should probably sit closer in casting cost to Flamebreak.

Yeah, true. Final Judgment as a scheme would be rather obscene.