OPML and Namespace

Dave Winer asks XML experts: can we put a namespace declaration at the head of an OPML file without breaking processors? If breakage of not even a single existing OPML app is acceptable, then the question can't be answered without actually counting the number of apps that breaks. But this can't be done because not everyone is paying attention.
My best informed guess is that this change will break some apps. A downside of simplicity in XML-based data format is that simplicity could mislead developers into doing task-specific hand-parsing instead of using fully compliant XML parsers.
I think it's more relevant to ask whether his immediate need requires namespace support. Looking at his proposed change (add ownerId element in the head section), I think just adding the element as-is will break fewer OPML apps than doing it the standard way using XML namespace.
Standards are useful but not when it hurts more than helps.