Seems like an interesting effort. A developer is building an alternative Java-based backend to Lemmy’s Rust-based one, with the goal of building in a handful of different features. The dev is looking at using this compatibility to migrate their instance over to the new platform, while allowing the community to use their apps of choice.
Rust is as much of a Java killer as C++ is. You could say Rust is the C++ killer, but I really don’t see how Rust would be that comparable to Java, which operates at a higher level instead of memory and pointer management. IMO, Kotlin is the Java killer.