Yeah butterfree is very cool in this meta. With accesses to powerfull moves like blue flare and boomburst, It's quite strong actually. It can be used as a sweeper, or a baton passer. Not the best, but has a nice nicheI've played this metagame for a few days now and I've noticed that Butterfree can make for a somewhat reliable Smeargle replacement when you have another "S" Pokemon in your party.
My Butterfree currently has:
Sleep Powder (learned)
Belly Drum (B)
Baton Pass (B)
Quiver Dance (learned)
Thanks to its ability Compound Eyes, the 75% accuracy of Sleep Powder is bumped up to 91% in the absence of Spore. Theoretically you could give this Butterfree a Wide Lens to amp up this accuracy even more, but then it wouldn't have a Focus Sash in order to have a guaranteed turn to pull off Sleep Powder.
This Butterfree can serve many of its teammates' needs. If you need a 4x Attack boost, Belly Drum will get it done. If you want a solid Sp Atk, Sp Def, and Speed increase, then you can use Quiver Dance.
However, this Butterfree has no attacking moves, so it will be completely shut out by Taunt. If it is the last Pokemon in your party, your opponent will automatically win. But, if you want an "S" Pokemon on your team that's not Smeargle, Butterfree is a solid choice.