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.
Depends on amount of technical debt really. Sometimes rewrite is the only way. But in general fixing things can be done. It’s just matter of time, focus and effort.