When you think about it, it's almost impossible for a top club to bring an academy keeper into the first team these days. No top team can risk having an unproven second choice keeper. One injury to your first choice and suddenly you're trusting a kid to immediately be good enough. From the perspective of the player himself, his development is going to be seriously damaged if he is promoted to sit on the bench any time before the age of, say, 23/24. You need to be playing regular football up until that sort of age to finish developing into a mature player.
So it's almost inevitable that the club instead signs someone like Lindegaard, who has finished developing at a smaller club, and has played first-team football for long enough to have proven himself to be quality. He's old enough that he can spend large swathes of the season sitting on the bench without his actual ability being damaged as a result.
The only way I can really see it happening would be the unlikely serendipity of the first team finding themselves in need of a first-choice keeper just as they have a star GK in the U21s reaching the stage that he looks ready for first-team football. For example, if someone like de Gea had come through the ranks at United, having a 'Januzaj 2012-13' type season in 2010-11. You're still taking the 'relying on a kid' risk, obviously, but this time it's offset by the incredible potential of the youngster in question. And because he's being promoted straight to first choice, rather than to be the back-up, he'll continue to get regular football and his development won't be impeded.