I am assuming the proposal is to knockout the gene Lim1, which in other animals, creates a brainless phenotype. You won't be able to swap a brain into this headless body (assuming it can fully develop), but this approach could be used for medical research and potentially solve the problem of organ donors, assuming it is ethical

Also, just because Lem1 creates a headless mouse doesn't mean it will do the same in Humans. But I suppose that's what the primate testing will reveal