The 5 year plan was never just about getting back to the Prem, it was about the club as a whole. This is emphasized by the fact that after our first season in League One Cortese said we were actually well ahead of schedule despite missing out on the play-offs. With this in mind, we probably still have another year and a half or so before he moves onto the next big stage.
If you ask me, the first part was all about preparing the club to challenge for the top 6. We've got a young, talented team and manager, training and youth facilities up there with the best in the country (as well as the youth players proving the investment was worth it) and a stadium that is perfectly sized for what we want to achieve.
Next part of his plan is most likely about actually getting into the top 6, and for me that is the biggest challenge yet - even more tough than getting back to the Prem.