Hi Nils,
While this is a development issue, an RPM diffing tool is in no way Fedora specific (I hope).
I think an RPM diffing tool would be most on-topic on rpm-list (out of the pool of existing mailing lists),
I have no problem continuing this discussion on the rpm list (although the question where this is most on topic remains), but I hope you don't expect me to go sit in an empty room and wait for people to start talking to me ;-) .
Bye, Leonard.