This could theoretically be done with stemcell stuff, but it’s not there yet. However, when we finally reach the point where we can infinitely regenerate our body cells, we’ll become effectively “ammortal”; unable to die due to natural causes (such as illness), but we will still die from other people (for example, a bullet to the head)
Besides that, I think nuclear fusion would be an incredible development if we can finally harness it to power our homes.