Well, there is nothing in the spec that says would forbid the JVM loading a ProgramLauncher.class file with a public static void main method, which will look at the program arguments and if it has something ending in .java, it will compile that file, and load the resulting class (current mode of execution).

Also, even if it might become a spec change (a language level one, not a jvm level one), it will be an additive change, at worst some new program won’t run on older JVMs, but all old program will continue to run on new ones.