As for what is stopping us: 1. Actually finding, isolating, and harvesting that virus, and 2. Proving that getting that virus doesn't cause some form of immun

As for what is stopping us: 1. Actually finding, isolating, and harvesting that virus, and 2. Proving that getting that virus doesn't cause some form of immune enhancement syndrome that would cause subsequent infection by a different coronavirus strain to result in more severe symptoms. (e.g., getting infected with one strain of Dengue fever causes lifelong immunity to that strain, but it also typically results in far more severe symptoms if you then catch a different strain). Immune system issues were identified with some earlier SARS vaccines but researchers discovered a likely way around it.