The pre-processor doesn’t simplify the language syntax! It complicates it, eg. by adding color as another type.
The structural changes around writing a class body rather than a whole class, adding default imports, etc. can be done without changing the underlying syntax. It’s something things like JShell do. And exactly what PraxisLIVE does for working with Processing code, which means it’s no more difficult than PDE to write code but all Java 8 syntax just works!