Great points! In reality I believe the goal should be to produce a healthy tortoise using the correct environmental conditions, as opposed to remedying the outward visible appearance using a topical substance like oils.The "coconut oil theory" is not widely accepted by many it seems. But i am seeing more and more examples where it seems to have merit in HELPING.
The issue is keeping new keratin growth, especially in younger, actively growing tortoise, from desiccating and drying too quickly. When the type of keratin that forms tortoise scutes dries out, it becomes very stiff, water resistant and strong. That become a good protective shield for a tortoise. But while the keratin is still forming and thickening at new growth seams, if it dries too quickly, it becomes stiffer and hardens before the seam has fully formed. So we are becoming aware it is important to create an environment for young tortoises where that drying does not occur.
In nature, growth in wetter times and staying buried or covered in leaf litter and deep in grass clumps does this. Young tortoises are rarely ever seen in the wild and very hard to find. The nest the mother dug and the eggshell protected the keratin developing for the embryo tortoise. Once they hatch, most will stay in the moist nest chamber until rain and moisture from above stimulates them to dig up and emerge. But then, they must find cover immediately. Not only for protection from predators, but to protect their develping shells (and themselves) from drying out. They seem like perfect little fully formed tortoises, but in reality, they are still too fragile for the environment they can find themselves in.
I believe we are just learning the extent of this. In captivity, we therefore need to find ways to help them continue that early development and create environments that allow that to happen. This is not just an effort to grow a "perfect" looking tortoise. That is what we see on the outside. But the drying is doing more than pyramiding the shell. It is also effecting the formation of the organs and functions of the tortoise. So for me, seeing how well their shell is developing gives me insight into how well the entire tortoise is being allowed to develop. Their entire structure and lifestyle has developed to preserve moisture. Until they are more fully formed, they must be much better about protecting themselves. Once their shell, and their organs and metabolism has grown to a more resistant level, they are much better equipped to be "out and about". I think this realization is helping us understand why we see so many baby tortoise simply "fail to thrive".
We can therefore raise the humidity in their enclosures. This helps keep the tortoise from desiccating. Not just the shell, but the entire tortoise. Same with daily soaking and humid hides or plenty of humid cover.
SO.. now to your question directly - Coconut oil may indeed help keep a tortoise's shell growing better as it does seem it should keep the new keratin from drying excessively and retain moisture. So in an effort to grow a pretty, perfect looking tortoise, it may have great added value. However, we must still be sure the inside of the tortoise is not drying excessively. So this could be a misleading "solution" if it ever is seen as a substitute for humidity. I don't want to just grow a nice looking tortoise. I want the whole tortoise allowed to grow properly during those early growing years. Coconut oil applied once or twice a week as a moisturizing agent for the shell would not interfere with and certainly should not replace the bath. Moisture is not absorbed through the shell. We are trying to keep the new growth seams from drying out and losing moisture. But we are also trying to allow the tortoise to drink and soak and absorb water through skin contact in the bath. The same with humidity in the enclosure. The shell, the skin, the eyes, the insides of the lungs as it breathes - everything needs moisture. Not just the shell.
My interest in pyramiding is not to grow a perfect looking tortoise. My interest in pyramiding is because the way the shell grows is our visible sign we can take note of on how the ENTIRE tortoise is growing - inside and out.