To put it frankly, it won't happen.
Not only because of the physical impracticalities but also the psychological cost that it would entail.
Body and mind are a necessary tool in the evolution of humankind since the beginning of civilisation. There are too much unknown about how the brain works within a body that it's not feasible to try to separate the two and say we'll be just a brain in a computer simulation la di da.
Makes for nice sci-fi but not for a realistic prediction about the future at the moment.