Tim, Mathieu,
this is not just a minor implementation detail. You are talking about introducing a completely different semantics for $0-symbols. Global symbol atoms, as they are defined currently, are immutable entities. Any Pd object may transparently store them, retrieve, etc.
that's exactly, what concerns me most ... on the other hand, a $0-symbol that's $0 is connected with a canvas that doesn't exist any more can't be seen as valid any more ... the question is how to handle this ...
cheers ... tim