From what I've read of it, Iphikrates' innovation seems to have been to devise a combination of kit (namely, longer spear) and training that allowed peltastai to be readily converted into close-order line infantry, ie. scratch hoplitai. So it wasn't about changing hoplites but peltasts - who were way more readily available. A way to create a "light hoplite" force on a budget, so to speak.

The attraction of this approach to the Macedonian kings is not difficult to see; they pretty much had no hoplites at all, but rather a quasi-feudal system which furnished them with lots of aristocratic cavalry on one hand and large numbers of psiloi levies on the other. There was an obvious shortage of line infantry capable of anchoring the line and creating a bulwark for the cavalry to operate around there, and it bit them in the ass often enough. Hence, Philip's further developement of the Iphikratean system to make lineholder pikemen out of psiloi skirmishers, which had the side bonus effect of allowing them to be deployed as light infantry with a simple equipement swap to boot...