All top teams already attempt this.
Problem is, identifying world class potential is hard, and getting them cheap is even harder.
The idea is to spend the transfer budget on them, another poster above who first suggested the idea said Ferguson spent about 50m on average on transfers over the last decade, if so, imagine if that money was spent on two players like Shaw, Rooney, Ronaldo or De Gea who had obvious world class potential as opposed to a lot of these squad players that never.
So if you can get them cheap then great but there is not anything wrong with paying up to £30m for them.
I'm saying nothing of the sort. You're basically advocating an Arsene-Wenger-on-steroids transfer policy. Which is a rubbish idea, just ask Wenger. Anyway, how do you identify a 'potentially world class young player', for every position, who still wants to come to you in the knowledge you'll ship him off as soon as you either find out he's brilliant or find out he's not?
I mean take the great forwards in the world today - Cavani, Falcao were unheard of whereas the likes of Benzema, Neymar cost ridiculous money. The likes of Van Persie, Suarez, and Ibrahimovic were spoilt brats / trouble makers who managers took a punt on but it certainly wasn't without risk.
You won't ship him off unless you have the Pogba - Vidal scenario, where it would make sense to develop Pogba now and sell Vidal using the funds to get players in other positions.
Also, my post was in response to somebody who suggested since Ferguson averaged about £50m a year in his last decade (according to another poster) imagine if we used that to buy only players like Rooney, Ronaldo, De Gea and Shaw instead of a Valencia or Young.
Arsene Wenger doesn't really spend £30m on world class level potential teenagers. So if you think (like Shaw) £30m is worth it then do it, if you can get them for cheaper like Ronaldo or even cheaper like Januzaj, also do that but as a transfer policy work very hard signing players with world class level potential. A Valencia, Young, Buutner, Bebe, Owen, Oberton, Diouf, Berbatov, Tosic, Alan Smith, Kleberson, Djemba-Djemba etc. would not fall into this category.
I think a lot of our squad players were cheaper and Ferguson liked his big squad. I'm not sure if we need as big of a squad as we have though and we could benefit from the quality over quantity approach. I think as a general rule, teenagers are good to target because you get so many years out of them, you end up getting value for money even if they don't achieve the potential but otherwise only sign a player if he has the potential in the manager's opinion to become world class.