Couldn't there be a way to extend and/or override portions of Parrot specifically for one's language-of-choice? This way, lots of communities can work together on relevant and mutually beneficial places and drop-in their custom code where it suits their language.
You can. You have two different ways of doing it: the first is to write your own low level opcodes, the other, and I think more powerful, is through PMCs. A PMC (Parrot Magic Cookie) is a basic type of your language (e.g. an Integer, a Char, etc.) with some operations associated to it that you can override. Operations include assignment, type conversion, invocation, your own methods and many more. After writing a PMC you can then "map" it to a core type. As an example, if you write a "function" PMC and map it to Parrot's "function" PMC every time the VM needs to create/use a function, it will use the one you defined instead of the default one. This gives a LOT of flexibility.
