Blakey is someone who could play anywhere. He can play forward (key or medium), could go on a wing and probably looked at his best during the u18 champs when he started at stoppages and won first possession.
Sydney probably will place Blakey where he is most needed. He might be viewed I'll speculate as something like a Sam Reid successor as more a CHF.
He's a definitely first round pick, could attract a top 5 bid. It would be a shock to see no one inside the top 10 bid on him. He's a clear top 7/8 talent this year.
This is just a guess but I think the Swans will play him as a midfielder in the first few years, at least until his body fills out. He would be a very awkward size to stop in the midfield and because he has the ability to play there it makes sense to play him in the midfield rather than keeping him in the forward line when he isn't quite ready for that position.