The UN report [1] says that if the world population switches to a fully plant-based diet by 2050, accounting for the expected growth in population, we would actually use less land and less water as we do now. So we could in terms of land and water use. Or do you mean some other reason why this would be impossible?

[1] https://www.ipcc.ch/site/assets/uploads/2019/08/4.-SPM_Appro...