To be clear, I am not anti-Lisp. I am simply trying to understand what Minsky is claiming. Specifically what he says about Lisp having an open future while C is subject to strange limitations and also what he says about Lisp being unique because Lisp programs can write other Lisp programs.
We've already been over Lisp macros vs. C preprocessor. They are completely different animals so comparing them doesn't get us very far. This also raises the question of whether Lisp style macros are necessary in C. What real world tasks could we perform with Lisp style macros in C that we cannot currently perform without them?
C standards are backward compatible so future compatibility is a non-issue. You're more likely to find breaking changes in Lisp standards than C standards.