[mindslight]

I'm arguing that (2) should be fine. Piercing the veil is only a concern if the managers/owners of the overarching LLC could be found liable. But this would be a bona fide business for them, so why should they? Piercing the veil of an individual series to go after the original uploader would be a definite possibility, but the whole point of this setup is for the original uploader to not have have to dox themselves to file a counterclaim.

Pooling like (1) might be an interesting approach to strengthen things further. You don't need to own a copyright to defend against a copyright claim, so the work merely needs to be licensed to the LLC series. A nontransferrable license to upload a work to a web host has little commercial value. In the worst case, a successful claimant would get the ability to contact webhosts to seize control of other accounts it then owns, and the ability to disrupt defense of other claims by seizing incoming funding. But given how useless such results would be, would it even be worth it for a troll to press that far?

You could add additional interested parties into the mix by playing the public good angle. Donate to this foundation to protect user generated content against SLAPPs, etc.