Well, i can tell you this much: Voulenteering in football/coaching with children from toddler age up until their mid teens is almost exclusively about moulding their future as a footballer (In addition to making sure they also have fun doing it). It´s very very hard in Norway, as we have strict regulations about children´s sports being competitive on any level. But what I´m saying is - you work with building the future player´s potential. The more you nurse it, the higher the potential gets. It´s all about mentality and a base of abilities making future progress possible.
So an increase in potential is both plausible, and possible, and something that´s being worked on at a daily basis all around the world. You have to build the player before you can mould him. Ability, wether it´s potential or current, as interpreted in a game like FM, isn´t there from birth. It´s created by verious factors