I agree there should be a youth league, but I don't think it should be for everyone. For many players, one team is enough, and generating more youth players than are already available would flood the system with youth players to the point of absurdity. Youth leagues should be optional, but available to teams with at least 15 players on their youth squad, and a specially appointed youth team coach. You can collect players through academy promotion and the market. However, I've always thought each time one upgrades their academy, it should raise the number of youth players that can be promoted per season by one. Good quality academies should be able to promote 10 or 11 players per season.
However, since only a fraction of all users will develop large enough youth squads to participate, the leagues should be continental rather than national, at least until a given nation has enough youth teams to form their own national youth league. This could be done using the nations in real-world confederations like UEFA, CONMEBOL, CONCACAF, etc. This would keep game times (and hypothetical travel times) reasonable. What we don't want are global youth leagues dominated by Thai clubs (there sure seem to be a lot of them), unless we live in Thailand or somewhere else in Asia. This could also serve as a foundation to organize regional champions leagues instead of the global champions league....
Having a youth team in a youth league on top of the regular team would not be a cheap endeavor. It would require additional coaches, would put added requirements and stress on existing facilities, and would thus surely increase their operating/upgrade costs. Of course it would also bring in some revenue, but the amount would be limited.
