Just Grass.
The type chart is incredibly imbalanced for Normal and Steel. Normal kills everything, Steel dies to everything.
Can anything survive an explosion without boosts?
Anything that could survive it before? Explosion no longer halves Defense, and there are plenty of Pokémon who aren't one-shotted by it, even if they didn't resist it. Normal had near-unresisted type coverage anyway. If you weren't Steel, Ghost, or Rock, you took neutral damage. Granted, Steel and Ghost have become quite prevalent (especially Ghost in this Generation), but they're hardly the majority of any tier.
Aggron is the only one I can think of hit 4x by Normal, since both Steel/Ghost and Rock/Ghost aren't currently used. If you have a team without Steel types, you're pretty much unaffected by the change, and Ghost moves (which are now everywhere thanks to the new Steel resistance loss) will destroy Normals just as Fighting used to.
There's only so much that it can do. It's best special attacks are blocked by Soundproof, and all of its attacks with drawbacks (of which there are a lot) still have those. Sure, being scaled for no Super-Effective hits for six Generations means that some of them have power that's a little on the strong side, but it's still nothing that most Pokémon can't take neutrally. Heck, most of them already do.
Nintendo/Gamefreak/whoever decides these things might have inverse battles available as a battle spot special in an upcoming season. That'll be a good way to push it.
Honestly, I think that the "single-NPC using the mode" was an indication that GameFreak is pretty much just trying it out, looking for reception. If people like it, I expect it to become as used as the other battle formats. Doubles, Triples, Rotations, and now Inverse.
I'm calling an Inverse Restaurant Menu in Pokémon Z.