These are just some ideas. There is absolutely no guarantee that any of them
      will ever be implemented.
    
- 
          Use SBO.
        
- 
          Allow more control over vtable layout.
        
- 
          Attempt to reuse sub-tables in conversions.
        
- 
          Allow "dynamic_cast". This requires creating a global registry
          of concept mappings.
        
- 
          Optimize the compile-time cost.