>if Web2 became a dystopic Zuckerbergia and Web3 is a disguised Cryptobrosia is there maybe a chance for a Web 2.5 that doesn't suck?

Nobody is forcing people to use Facebook or any of Facebook's family of apps. I personally don't use FB or any of its apps for the last 10 years and I'm totally fine.

>What would be its building blocks? IFPS, Activitypub, XMPP, Matrix?

IP, TCP and HTTP are not going away anytime soon. Nobody really knows how would next stage of WWW look like therefore you can't even think about candidate protocols and standards.