It depends on what you mean by "replace".
The Fediverse may cause centralized social-media networks to join the Fediverse.
There are some hints of that happening now.
Facebook / Meta has created a new social-media network that is part of the Fediverse.
Tumblr and Flickr are said to be joining the Fediverse.
So, some "popular social media" may become one with the Fediverse.
@dookie
What are about Mastodon, that you like, that Pleroma lacks?