Surely they could. But even if they accompany the PS5-release with a Nintendo console which has the same specs, it will go differently. 3rd-parties would port some stuff. It would sell bad (because the people wanting 3rd-party getting the PS5) and 3rd-parties therefore would neglect the console. In the end it would be Nintendo-only. So, while technically it would be easy, they would fail with such a concept.