I wonder if there are concrete use cases for loading/dumping basic types.
I see two options here:
1) we decide that load/dump should accept and produce only complete json object and go through a deprecation process, raising warnings first and errors then;
2) we decide that the correct behavior (loading/dumping basic types) is fine and that should be up to the user to check if the document has an array/object at the top level and then just document it (if it's not documented already).