I hope this protest has a positive effect, but cynically I'm pretty sure it's going to make a small splash, and then fizzle. Any popular subs that go dark too long well get sudo'd back online I'm sure.
My pipe dream is, instead of a black out, all the users come together and spam NSFW content on all the major subs to hopefully piss off their advertisers. Collaboration on that scale will probably never happen though.
If you really want to hit them, just make a concerted effort to request GDPR data for your user. It's perfectly legal, it costs them time and money, and it may also actually benefit you to know what kind of data reddit collects about you.
At some point, it may even become a nice tool, say if someone creates a way to import that data into e.g. the fediverse or tilde or something similar.
This is why the protest is limited to 48 hours at first, because that's the known "safe" duration. See what happened to r/news a couple years ago.
The two-day blackout isn't the goal, and it isn't the end. Should things reach the 14th with no sign of Reddit choosing to fix what they've broken, we'll use the community and buzz we've built between then and now as a tool for further action.
Neither am I. I think they are going about it the right way. I just think Reddit is intent on Digg-ing themselves a grave and I don't even think they understand the consequences of their actions. I'm sure they did some math on losing 3rd party app users, but I think they severely miscalculated on the moderator and accessibility fronts.
In the U.S., Section 504 requires web services to provide "individuals with disabilities an equal opportunity to participate." For now, Reddit has complied with that because third party applications using the free API constitute an equal opportunity (actually, it's a better opportunity - even better). However Reddit's website and first-party application do not work with screen readers. If Reddit goes through with this, I fully expect them to be sued. I wouldn't be too surprised if they weren't even aware of this, because the relevant communities have quietly used third-party access since ever.