WASM uses a block structured IR (that is, no arbitrary gotos) and I would characterize it as in between of the [serialized] Juice AST and the flat Java bytecodes.

From the compiler's point of view the Juice AST is the same as source code so I'd expect the Juice JIT to have slight more code generation flexibility than the type-erased WASM.

No, it was an Applet from Java era.