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.
Anyone can quickly learn how to solve some code challenges in a new language.
It’s a completely different story to learn how to write long lived enterprise scale programs that can grow with multiple independent contributors. This takes a lifetime to learn. More people have more experience to do it with Java.