I have been working on a tool called Autoforwardportergit for automating the process or merging downstream changes with new versions from Debian. A downstream in this case could be anything from your private modified versions of some packages to a major derivative distribution.
It was created for use by Raspbian but I have been working to generalize and document it such that others can use it to. I have just written a tutorial which demonstrates how to set up and use it. At this point I would really appreciate people trying it out and telling me what they think. It can be found at https://github.com/plugwash/autoforwardportergit . The tutorial can be found at https://github.com/plugwash/autoforwardportergit/blob/master/tutorial/README.md If there is sufficient interest I will package it and upload it to Debian.
