The problem is that by adding transient properties the generated metamodel class is not canonical anymore. The spec says:

For every persistent non-collection-valued attribute y declared by class X, where the type of y
is Y, the metamodel class must contain a declaration as follows:
public static volatile SingularAttribute<X, Y> y;

The problem is that a transient is not a persistent field. I am not convinced yet that it is a good idea to use the model for something else than type safe criteria queries and whether it is worth to break the canonical rule.