Our next U21 manager should be someone who the FA view as being the next England manager. He needs to have a defined playing style and be able to get it to work effectively. So basically they manage the U21 team for the next 3-5 years til after Euro 2016 or WC2018, and then (if they're doing well) they take over the England job, and play the same way. It would be a natural progression that would allow the players to become used to a playing style and playing it together. When I say a defined playing style, it doesn't even have to be pretty tika-taka stuff, it can be Sam Allardyce for all I care, as long as it is something that can work on the international stage.
That said, I would prefer good passing football as opposed to hoofing it up, and I think we have the young players capable of doing it with the likes of Wilshere/Hendo/Cleverley/Rodwell. But the point is, when have any of those players EVER played together? I don't think they have, despite being similar ages. Players should be kept in the U21's until they are no longer eligible, unless they really have the ability to make an immediate impact and offer something we don't already have in the senior team (eg, Owen in 1998, Rooney in 2004).
I also think PL teams should be required to have at least one English/Welsh U21 player in their starting 11, and at least three English/Welsh U21 players in the matchday squad (starting 11 + subs). I added in the Welsh bit because it would probably be a bit unfair to expect Swansea/Cardiff to play English U21 players.