When you see Barca bringing through the likes of Iniesta, Xavi, Fabregas, Pique, Busquets, Messi, etc... it has to be possible to do it here too. It just depends on how committed the club are to achieving success that way.
Players like that don't go on trees. How many have Barca put through since then? They can't get them in the team. It was a one off generation.
Why haven't United kept on bringing through players of the calibre of Beckham and Scholes from that 92 youth side? Because they aren't there. The best they got through was Pogba and Ferguson messed that up.