Voila. Now the HTML response and the XML response refer to the same object. The XML client gets the field names and types, and defaults for the field values to boot. And we didn't even have to touch the Rails core.
Another reason this is good is that default values for attributes (at the DB level) will be included in the schema XML, which is definitely desired.
I played with exactly this last night, and I think it *is* the better solution, and of course far less work. The major problem is that this won't include any associations, even if :include is passed as a param, because all the associations are either an empty array or nil. Possible solutions are to add an :include_associations or :include_empty argument or something to to_xml, or to change to_xml's default behavior to include associations in the XML when :include'd, whether they're empty or not.
I'm starting to think that this may be unnecessary. Create/update requests don't need to be sent that include associated data -- those can be taken care of separately, with create/update requests to their own controller. I'm not set on this, and maybe associations should be included, but I think it's worth it to take the easy win now and get a schema with all attributes. I'll make the patch to add these lines to the scaffold_resource generator.