Comment 9 for bug 332116

It occurs to me that my suggestion wouldn't work as-is simply because the repo already has that first revision recorded with one parent, and you can't go and change the parent. so you'd need to go and define a new mapping, just to support the new semantics for svn-upgrade (which would force everyone to run svn-upgrade again).

In which case, what you've suggested probably makes more sense as a long term solution. If I understand you correctly, it might even remove the need for running svn-upgrade altogether?