MaxY
Devil May Cry
A mixture of both.
Some players will emerge for whom we don't know yet.
And some of the current players who are just very good today (I will say a random example, Dybala) may explode in 1-2-3 Seasons in some big club and become new superstars.
For example, if Real will win La liga or a CL in the next 2-3 Seasons, then some new leaders, like James, Kroos, or some new random guys, will become new Ronaldos, Bales and similar.
Also, new superstars from Argentina, Brasil always emerge.
So, it is extremely hard to predict today who will be Ballon'D'Or contender in 4-5 Seasons (after Messi and CR7), except for obvious choices like Neymar.
But you will see, in a few years, if you will look back to 2015', that you will say: Wow. Who would have predicted back then that these guys (in 2020) will be in top 3-4 players in the world suddenly?
(Just remember how Pogba turned from a 4 Million to a 100 Million player in 2-3 Seasons. Or how Pique turned from a poor defender from Man. Utd into one of the best defenders in the world. Some players just "explode", 1 out of 10, or 1 out of 100 players with potential)
But again, don't worry, new players always emerge.
For example, just remember, till the summer 2016, at least 2-3 new superstars will emerge, like Pogba, Depay, Dybala this summer.
Some players who are just good/nothing special today=will explode in 2015/16 Season and will turn into a 30-50 Million players whom Barca and Real will want to buy...
I don't think Pogba exploded from 4 M to 100 M, it's just that the market got so inflated. Pogba is nowhere near 100 M.