If this 1.6L T-GDi engine is same as what Hyundia has been offering since 2011, then there is plenty of UOAs and owner testimonials indicating that this engine runs best (as far as wear, valvetrain sounds, oil consumption, and fuel efficiency) on 40-grade oils.
With this in mind I wouldn't allow the dealership put 0W20 in there. Unless they sign a notarized form that they take full responsibility for any engine damage due to lower viscosity.
If one day you start changing the oil yourself, or get a trusted mechanic, then I'd recommend going with an oil that meets high-standard certifications such as Porsche A40 or MB 229.5. That would be oils like Mobil 1 0W40 or Castrol Edge 0W40.