I think a "down-vote everything" strike could be highly successful. As long as enough users participate, it could cripple subs whose moderators didn't choose to participate. And it is fitting. Reddit is trying to charge its users for content and data created for free by its users, so why shouldn't users make that data junk for awhile to make a statement?
I suspect Reddit already has protections in place against this type of coordinated attack, as it would look exactly like when a whole sub (or 4chan) decides to brigade another sub for some other reason. There’s probably a hidden limit somewhere that when you downvote too many things at once, those vote become shadow-votes that don’t really count anymore.
For instance, what do you think about an "inverted-voting" strike instead? Everyone on strike does things roughly as normal, but swapping most of their down votes for up votes, and visa-versa? That way, people on strike will continue to vote about the same amount as before, and in the same subeditors as before, so it would be harder to identify them. The hope would be that although Reddit could do work to clean up the voting data, it would be annoying & take time, and presumably still end up as significantly lower quality data than they had before.