It looks interesting, but then one would have to define a normalization for the AST - either something like an XML printout of the AST, or a standard formatting

It looks interesting, but then one would have to define a normalization for the AST - either something like an XML printout of the AST, or a standard formatting for source code (perhaps whitespace-only minification?). It would also pose an issue when presenting code in "dumb" media (eg. a txt file).