ActivityPub gives me hope for the future of the Internet. I was able to completely replace Reddit with Lemmy after the exodus last year. I never used Twitter, but Mastodon seems like an alternative that’s gaining popularity.
The one that seems the hardest to replace is YouTube, since hosting and serving video is very expensive, and many creators have come to rely on monitization.
I’m not sure about I2P being an alternative to the clearnet. It helps prevent censorship, sure, but I don’t see how it provides anything that you can’t do on the clearnet already, other than anonymity. It’s also much harder to set up than Tor for non-tech savvy people. Anyone can already host any website they want on the clearnet.