Hi,
right 
ConstraintValidatorFactoryImpl is not final, but if you look at the actual code 
getInstance  does not much:
Code:
   public final <T extends ConstraintValidator<?, ?>> T getInstance(Class<T> key) {
      return ReflectionHelper.newInstance( key, "ConstraintValidator" );
   }
Just implement 
ConstraintValidatorFactory directly.
Regarding 
connection(), this call is indeed deprecated (for a long time in fact). However, there is no real alternative atm. So the connection part still holds, only the factory code needs to be adjusted. Feel free to leave a comment on the wiki.
--Hardy