I don't think Luke will be leading an academy. I think he will have left everyone, living remotely like Obi and Yoda, but for other reasons, something like how the dark side affected him and he feels like the world can and should go on without jedis or siths, so he can be at peace.
But now he will have to pass on what he learned to an apprentice, because a new threat has arisen.
I think this will be done because otherwise he would need a wife and probably some kids, which would be too much ground to cover or to not cover. So making him a hermit is more appropriate, it allows us to pretty much see Luke right where we last saw him, at peace, but with nothing missed in all those years. Han and Leia though will obviously be a different story, but you can't damage the icon that Luke is by having anything having happened significantly since the original trilogy. In that scenario Luke would be the embodiment of a direct link to the original trilogy, which is exactly what is needed for the series. He's basically a figure of purity at the end of RotJ, you can't really change him, other than having him in a sort of peaceful symbolically-cryogenic state.
It's like why at the end of The Matrix trilogy, Neo is taken away. Same reasoning. Same reason Jesus goes to heaven. You can't change the hero, he has to remain who he is until he is called upon again.