I think GvR's special expertise is more in the 'user-interface' of programming languages than in their implementation. The whole point of Python, really, is to put the former before the latter; which is exemplified in GvR's 'readable-stack-traces before fancy-features-in-the-implementation' reasoning on the present point.
Even if you’re designing for professional programmers, in the end your programming language is basically a user-interface design. You will get much better results regardless of what you’re trying to do if you think of it as a user-interface design. Alan Kay http://queue.acm.org/detail.cfm?id=1039523
