BTW I would like to see in OOP languages ability do redefine build in concepts (inb4 lisp).
As example: I have number "13", now I would like to add method to all numbers, say be_in_8_base_now, and be able to write sth like 13.be_in_8_base_now(). I would also like to completely redefine what numbers are, eg, to be able to write them in any base or form, that I created (I know, it would be hard to parse).