Acts of Congress, at least the important ones, are directives to the Government Printing Office to make changes in the US Code. In a very real way, they are patches. Even without a formal API, couldn't someone extract the content out of the existing ASCII document representations of the US Code, and then extract the contents of the existing copies of bills before Congress, and literally show the diffs in line? Compare this version to that version, etc? It seems like a lot of the information is technically "transparent" if you read a chunk of the Federal Register, but what we need is better version control. I hear there's a pretty good version control system available for this kind of stuff. And I'll bet GitHub could handle surges in site traffic better than the GPO.