I am not a fan of Java. However, I think that you are 100% correct. This is a potentially very useful stack to have available and I hope that the two projects track together well.

This project has potential for high velocity development that Lemmy will never be able to match, purely because of the languages. Rust is, factually, slower to develop in than Java, even for experienced devs. Add to that the greater population that is comfortable with Java, and you have a recipe for really pushing interesting things and innovating quickly. Possibly establishing a relationship somewhat like Debian Sid to Debian Stable. It could also be interesting to have some low-level, Rust modules that are shared between the two when Lemmy gets to 1.0 (API stability), if there is something that is more optimally implemented in Rust but that would introduce more coupling.