Nothing, is going to replace Twitter, Twitter is not doomed. Moving off of Twitter because you don't like the owner is fools errand. You are either looking for an echo chamber that is tightly censored like twitter used to be (congrats on keeping your ignorance and refusing to listen to the other side all while virtue signaling how open and tolerant you are, when really you are just blowing smoke up your own ass), or you are going to end up a platform that has hardly any censorship at all and allows all the shit you are so mad about that is now back on Twitter.
>To kill it in the same way Reddit killed Digg
Reddit didn't kill Digg, Digg shot themselves in the head.