The problem is that essentially all systems that are tolerant to some faults generate different faults.

This is the major cause of the diseases of modern civilization, including degenerative diseases such as Alzheimer's.

When an organism enters the “fight or flight” state, (as when running from a bear), where to be caught is certain death, being “fault tolerant” in that case means turning off repair so as to divert resources to immediate consumption. A few extra molecules of ATP are wasted if used for healing if the bear catches you, but if healing is turned off, that ATP can be diverted to the legs and used for a few more steps and potential escape.

The brain (and all tissue compartments) exhibit what is called “ischemic preconditioning”, where several brief exposures to ischemia induce a state where the tissue compartment is much more resistant to prolonged ischemia than without the preconditioning. My interpretation of this universally observed behavior, is that brief periods of ischemia induce physiology to change state to a state where ATP consumption is lower, and so the loss of ATP producing substrates (blood and O2) is better tolerated. Resources are diverted from long term needs (maintaining DNA error free for example) to short term needs (staying alive for the next few minutes). During an ATP “crisis” (where there is not enough ATP to do everything that the organism would like to do), ATP consuming pathways that take longer than the duration of the crisis can safely be turned off and any ATP they would have used can be diverted to surviving the short term crisis.

Can the ischemic preconditioned state be maintained long term? Pretty obviously it cannot, otherwise organisms would have evolved to be in that state continuously (so more resources could be devoted to reproduction), and so would not exhibit ischemic preconditioning.

There has to be a hierarchy of physiology which prioritizes survival over repair of organs, and repair of organs over repair of DNA. Once the DNA starts to pick up errors, it is a one-way street to degeneration and death.

The problem is that in evolved organisms, these different pathways are all self-regulating and they are regulated to the priority hierarchy that evolved, which only prioritized survival leading to reproduction.

It should be possible (in principle), to design an organism from scratch, but the stress responses that program the ATP hierarchies are from such deep evolutionary time that a non-aging organism would really need to be designed from scratch. Even bacteria prioritize survival over maintaining DNA fidelity. An organism that prioritized long term survival over short term voluntary activity would have to be pretty clunky. If you spend 10x more on maintenance and repair, you can probably get a multiple of lifespan. But that increased maintenance has to be done for the whole lifespan, not just the increment. That is mostly what basal metabolism is now. You can't increase that by 10x, you have to reduce the part that is not devoted to repair.

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The firefly is capable of producing a "cold light" with a wavelength from 0.00051 to 0.00067 millimeters, pale greenish-yellowish with a light efficiency of 96%. The ordinary incandescent light has an efficiency of roughly 10%, most of the energy being wasted as heat.

The firefly goes all he way from chemical energy to light at 96% efficiency if we could approach that it would be amazing. I think all animal must be able to go from chemical energy to electricity at better than 96% efficiency wow.

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You should include “fault tolerance” in your list. An example of fault tolerance is missing both legs. You can achieve the same overall goals, although perhaps not as efficiently or using different techniques.

Wouldn't that fall under redundancy? You have backup systems (arms+wheelchair) in case the primary system (your legs) fails.

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Carroll is absolutely right. So far, everything "nano" is merely a buzzword with little to show for all the hype and there is nothing to indicate that this will ever change. Unless we can come up with an alternative (say, silicon-based) life forms, those wonderful nano machines will go the way of jet packs. In contrast, synthetic carbon life sounds actually doable. Problem is, de novo designing new life with precisely required outcomes is of the same difficulty as accurately predicting weather in the range of months and years. Not gonna happen in our lifetimes (if ever).

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Another way of solving it is to keep them isolated to gentler conditions. Artificial mechanisms that don't rely on the presence of liquid water can survive and thrive at very low temperatures, and under a vacuum. While these wouldn't be suitable for medical purposes (except perhaps in cases of cryonics repair), they would still be useful for manufacturing.

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You should include "fault tolerance" in your list. An example of fault tolerance is missing both legs. You can achieve the same overall goals, although perhaps not as efficiently or using different techniques. Reliability seems more like preventing damage (like having a rib-cage) than dealing with damage, but perhaps still deserves a spot on your list.

When to redesign? That's a big question and although I don't have a problem with the part you're addressing, there are many more factors to consider.

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