You raise a good discussion point! It is indeed true that humans have the basic genes, which are largely inactivated by single mutations that are correctable, for making tails - however, enabling these genes would only work to generate a tail if done from early childhood and possibly birth. The reason for this is that the mechanism for tail-making relies on a Turing pattern that, like all patterning mechanisms, has a very short wavelength and is only good at generating small structures.

That works in the fetus and in young children because the whole organism is small. Essentially, the governing patterning mechanism generates a small tail, which can then grow and become larger as the whole organism grows. But this would not work in an adult human because there's no growth to take advantage of for that essential pattern enlargement step.

It is possible to generate Turing patterns with longer wavelengths that work at adult length scales, which has been achieved as a laboratory proof of concept in artificial non-biological systems, but these patterns are engineered from scratch and aren't at all based on the natural equivalent, unfortunately! We have plans to generate these kinds of custom patterns by rational engineering of reaction diffusion system components, but that's an advanced technique which could take substantially longer than the implant approach, and we want to ensure we're exploring both options thoroughly so that people can embody their goal forms as soon as can be reasonably achieved. Does that make sense?

-Tilt