Seems to me like the plan is actually on track, but will take some time to come to fruition.
If we produce just one academy graduate a year capable of breaking into the first team, it's not unreasonable to expect half of the squad to be graduates of the academy in 5 or 6 years time.
Of course, we may face retention problems with some of the real gems, but I imagine the Cortese plan is to make a better fist of keeping the Walcotts, Bales and Chamberlains, which is obviously more feasible in the PL.
Additionally, some youngsters might "break into the first team" without really becoming an integral part of it. Lallana has managed it. So has Shaw. JW-P? Looks promising, but am only about 50-50 as to whether he will become a regular starting player in future. Ben Reeves has fallen short, as has Sam Hoskins. Calum Chambers? Who knows? Jury is also out on Jack Stephens.
Nevertheless, I can well imagine that in 5 years time, an average of 9 of our 18 man squad will be academy products. It at least seems something worth aspiring to.