It is nothing more annoying than to read uneducated posters going nuts about Nike shoes working like springs like it's some kind of unseen phenomenal technology that they have invented. Springs by definition are devices intended for storing mechanical energy and so works any elastic outsole of any shoe ever made intentionaly or not.
For those of you who have hard time to grasp this let me illustrate it. If you squeeze the outsole of any shoe between your fingers you are storing the mechanical energy which is released once you release the fingers and the outsole starts to return to it's original shape. If you apply force and bend any shoe under angle with your hands it's outsole stores some of that energy which is again released once you let go and allow the shoe to regain it's shape. Both of these illustrations are clear examples of an elastic spring in action. And it's built into any shoe intentionaly or not since forever. Now I haven't got a chance to hold a carbon plate in my hands but I'm quite sure that they also are able to store some of the mechanical energy and act like elastic spring if being bent under angle which is exactly what you do when sprinting in one of those track spikes that have built-in "spring" since 1990s.
If you have followed this far you should now have general understanding of how your shoe works like a spring each step you take. It doesn't matter if it's a ballet shoe, a running shoe or an army boot, it still has characteristics of an elastic spring. Just that some of those springs are more efficient than others depending on material used for outsole. But one thing is pretty clear across the stack of running shoes and that is the more premium the racing shoe the better at returning energy it is, the more efficient spring characteristics it has.
So does Nike shoes posses a spring like characteristics? Yes.
Does Asics, Reebok, Saucony, New Balance and other shoes act like springs? Sure they do
Are Crocs one of the best running shoes in terms of energy return? You bet they are
So why is it illegal for Nike shoe to have a spring-like characteristics and not illegal for other manufacturer shoes to have the same spring-like characteristics? If this isn't bias then what is it?
Strictly looking at IAAF rules all shoes assist in performance gain since they all have spring like characteristics. Nike has taken efficiency to the next level and this is why they are witch hunted now but generally any shoe falls in the same bucket.
I see only three options for IAAF:
1) ban all shoes
2) put restrictions on how much energy a shoe is allowed to return under specific conditions just like it's with tracks - VF can't be banned in this case as this would automatically invalidate results set on tracks in the last 20-25 years since most probably track spikes posses superior elasticity characteristics
3) do not do anything