I guess I should have been more clear.
How about ESRI changing the specification of ESRI FGDB, ArcSDE etc to allow clients to specify that a FGDB file is only allowed to accept a single LineString or Polygon.
We as developers have no control over what kinds of data external users create in the FGDB format using tools such as ArcMap.
It could be something as simple as adding extra metadata in the XML description (e.g. <singlePartOnly>true</singlePartOnly>) that would be enforced by editing applications such as ArcMap.
Pass this along to whoever make decisions in the file format.
Multi part has caused my client (a large regional government ESRI licensee) a lot of hassle when accepting data from external contractors.