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.
That’s not applicable. Sublinks is using the same standard as Lemmy/kbin/mbin, i.e. ActivityPub. In a decentralized system based on an open standard, plurality of implementations is a good thing. We shouldn’t want lemmy to be the only one.