I would love to have a Java compiler with the capabilities of the .net compiler. To make incremental builds to aid code completion including type information, looking past simple syntactical errors, fixing them, and continuing compilation.

Currently, this is “magic” embedded in eclipse, IntelliJ, and maybe a bit in the vscode plugin. Imagine having a Java LSP running that can provide all this information while typing.

.net has had this for ages. From a language design I think that is wonderful.

The counterpoint is that Java has so much SOTA GC work precisely because the language makes writing efficient code that doesn't heavily tax the GC basically impossible.