Frank,
There was a dicsussion on this subject about a year or so ago following a question I asked about this issue. I will try to find the link.
The issue was discussed but the decision was taken to do nothing because there was no obvious solution that was acceptable at the time.
It was considered unacceptable to have code (be it kernel code or other package code) deleting data that belongs to a package.
Now that callbacks have been developed and are widely used it does seem sensible to require each package to provide a callback for user deletion.
However this is unlikely to be trivial and there will be issues. For example where objects are connected with multiple users and where packages are tightly integrated together when installed together but can exist seperately.
