I was recently pointed at a talk given by Guy Steele (who, amongst other things, co-invented Scheme), given at the 1998 OOPSLA Conference, entitled Growing a Language.

In it, he talks about the need for Java to add features that will allow the language to grow as users add to it, specifically suggesting two features (one of which has been added, albeit poorly, and one of which is still yet to be implemented); but the real value of the talk is not what he says, but in how it is presented: whilst giving that away would be entirely unfair, I recommend watching at least the first 10 minutes of it, to allow you to figure out what’s going on.

So, if you get a spare hour in the near future, I suggest you watch it.