Type :
  'type' name=ID 'properties {'
    properties+=Property
  '}';
Property :
  name=ID;

// object must inherit from the properties of its type
Object :
  'object' name=ID type=[Type|FQN]';';

SomeRule : 
  'somerule' prop=[ConcreteProperty|FQN]';';

// the ConcreteProperty is the object I manually create from code (exists in the metamodel), which inherits from Property and augmented with a feature 'inObject' -> Object

// such that I may be able to do something like in the following concrete model snippet

type MyType properties {
  aProperty
}

object myObject MyType;
somerule myObject.aProperty; 
// the proposal provider gives the right stuff, but it is marked as error with "couldn't resolve reference"

FQN:
  ID ('.' ID)*;

@Override
protected IScope getGlobalScope(Resource context, EReference reference) {
	return super.getGlobalScope(context, reference, 
                  makeFilterForAccessibleObjects(context.getContents().get(0)));
}

private Predicate<IEObjectDescription> makeFilterForAccessibleObjects(final EObject context) {
  return new Predicate<IEObjectDescription>() {
    @Override
    public boolean apply(IEObjectDescription input) { 
      /* some code to only accept elements from the model and imported models */
    }
  };
}