Michael, you're a genius!
Here is a couple of demo short scripts for generating and applying deltas between two rpms.
This is so unbelievably simple that for a while I thought you were pulling your own leg.
All one needs to do is bundle the two deltas with a text file (or xml if you want to be fancy) describing the versioning and let the script handle the naming.
All this needs to be used is an extra branch for deltas, next to the updates branch. And I thought xdeltas would be too expensive. I guess minigzip changes all that. It's unbelievable.
Bye, Leonard.