First of all, and obviously, Nostr can't replace anything which is about social networking, with a few exceptions.

Nostr also can't replace anything which requires more secrecy than Nostr can provide, since all events are public (even though the content can be encrypted).

Nostr, at this stage, is only really good for distributing text. Images on Nostr are being distributed trough HTTP with links to centralized platforms which are not resistant to censorship in any way. It may be that Nostr users choose image hosting platforms that have permissive policies, but that's a different point.

Nostr also can't replace anything that, for whatever reason, requires consensus, since relays can host different content.

Finally, I don't believe Nostr, or really decentralized protocols in general, can replace centralized social media platforms. I do want Nostr to succeed, but I think that'll make it popular along side centralized platforms, not fully replace them. The reason is that, while they may on the surface do a lot of the same stuff, they can't do everything *as well*.

Reactions (emojis and other stuff) will always be somewhat messy on Nostr, to mention one.

When a new technology comes along and gets adoption, sometimes reducing the use of some other technology, many think the old technology is falling out of use. And, as we see with programming languages too, for instance, this very often turns out not to be the case and instead the two things coexist.

I think that's the case with Nostr. It won't replace anything, but it will be great for a lot and I want it to succeed.