To open today's discussion, it is worth noting that any group that starts in on growing human clones that lack brains should expect to be promptly vilified and shut down by near any of the world's governments. The following discussion involves numerous projects that are already entirely illegal in most of the world. There is a very low tolerance for ethical experimentation with human tissue, unfortunately. That tolerance grows slowly over time, but we are certainly nowhere near the point at which entire bodies could be built in artificial wombs without a great deal of opposition at every step of the way.
It does seem worth talking about this prospect, however, because it is one of the technologically feasible approaches to evading the age-related failure of the body. Grow a clone without a brain, waiting the necessary years for it to be mature enough to use, transplant the old brain into the new cloned body, or transplant the head, a comparatively easier task, and then regenerate and connect the nervous system, vascular system, and all of the other items that pass through the neck into the head.
The long laundry list of capabilities needed to enact this course of action might be shorter than the list needed to repair the existing body, rejuvenating it. There may be less development and discovery required. I should say that this is not an assertion - it can be argued either way, and there is a great deal of uncertainty.
Firstly, there is the question of how to grow a new body without a brain, or at least without the parts of the brain that host a mind. This happens in the rare condition called anencephaly, a severe neural tube development disorder. The resulting body isn't a human, it is tissue without a mind. The causes are not fully understood, but researchers have looked at mutations in the MTHFR gene, with some compelling case studies. There is a path towards being able to create anencephaly to order in order to ethically grow mindless bodies.
Artificial wombs would be needed to generate replacement bodies at scale, and this is another field that in and of itself could be highly beneficial as a reproductive technology, but suffers its own restrictions on development. Researchers are thinking on the topic, however, and again there is a path forward given the present state of knowledge. The techniques needed to support brainless bodies after the initial development stage in an artificial womb are more of an unknown, given that natural anencephaly leads to rapid death after birth, but it seems plausible that many of the established techniques for brain dead and coma patients could be adapted to this use.
Separately, head transplantion in human patients is discussed in medical circles. It seems likely to happen at some point given the slow progression towards greater acceptance of procedures that provoke discomfort. If heart transplantation, why not body transplantation? Head transplantation has been carried out in animals, and there is a robust understanding of the challenges involved. The research community is a long way from what might be called reliability in producing a successful outcome, however. Further, the problems yet to be solved include producing a functional connection to the nervous system, a problem that might be analogous to that of repairing a severed spinal cord via regenerative therapies, or may be more complex due to individual differences in nervous system development.
Brain transplants are a much more speculative prospect. They have been carried out in primates, but the issues to be solved in moving a brain are manyfold more challenging and require a great deal more research and development. Nervous system tissue is fragile and non-regenerative. Still, given a focused program and significant funding, this is really just a matter of work, given where the research community stands today.
To my mind, the greatest objections to putting earnest effort into this line of work are that: (a) the damage of the aged brain will still need to be regenerated in some distinct way, restoring a youthful body will only go so far in term of restoring the environment; (b) major surgery in old age is highly undesirable, with a high risk of death through complications and stress; and (c) the expense of growing a body to sufficient maturity, for years, has the look of being very high in comparison to the expense of whole-body rejuvenation therapies. Rejuvenation of the brain will likely require technological capabilities that will enable rejuvenation of the body to a similar degree. So why not just aim in that direction to start with?
That said, the pieces of the replacement body puzzle are out there, waiting for someone to pull them together. Stranger things have happened.