Bugs like 806253 come up fairly regularly in unstable: two packages contain the same file, but don't have a Conflicts or Replaces relationship. Renamed packages seem like the most common case, though this can happen other ways as well.
The archive software already does a variety of checks on packages before accepting them into the archive. Do we have enough data and metadata available that the archive software could automatically reject uploads of .deb files that contain the same file path as another package without a Conflicts or Replaces expressed against that package? - Josh Triplett
