Wasm composes in the way that the JVM/SecurityManager did not. You can implement your proxy functions in wasm, not only defining the set of functions that a Wasm program uses to talk to the outside world, those proxy functions that you pass in can also be implemented in wasm inside of another context.

Wasm can learn from the JVM for sure, but if you went almost 30 years back in time, you would have some great tricks to teach the JVM, learned from Wasm.