For each centimeter of elongation in soft tissues, the main component is new growth but not all, a percentage is simply stretched tissue and would remain than way for many years or even a lifetime, and this percentage increases exponentially.
That is why, among other things, complications and recovery increase exponentially the more one lengthen, 16cm (in 1 segment) can only be done safely in people with dwarfism, since their tissues are compressed initially
and as others have told you, the biomechanical component would be compromised
no respectable doctor would allow you to do this plan, imo
I highly doubt that the tissues don't adapt along the way, after some point the strain becomes unbearable so they forcefully extends to adapt themselves better (or you can have a surgery that forcefully releases tension). But note that I haven't studied this yet so can't back it up, just my opinion.
There are people who lengthened 12 cm in a single surgery on this forum, so naturally this implies that if you make this process even easier (obviously, lengthening the same part two times is safer than lengthening in one go), you could gain even more on a single bone. So no, I don't believe this works only for people with dwarfism.
Speaking for biomechanics, I don't believe it to be a great deal (who cares about how fast you walk or how much you can bend your knees, anyway?)
Third, I emailed many doctors and the absolute majority are willing to do surgery on the same bone, furthermore doctors don't control how much you lengthen, after the surgery they can only give you recommendations.