Can we warn the user when they are running into the elementFormDefault="qualified" problem

It is common (and perfectly legal) for users to not include elementFormDefault="qualified" in their schemas and end up with the default value which is "unqualified". But often users don't realize the impact that this has on the requirements for namespace prefixes for local elements when interpreting the instance doc (a common mistake is to put xmlns="XXX" in a global element in the instance doc which then causes the local elements not to be picked up because under elementFormDefault="unqualified" they must have no namespace).

Is it possible to warn them if we are seeing an instance doc that would fit the schema if elementFormDefault="qualified" was there? (Would need to consider what the perf impacts of this would be too).