What really should've happened is have Rey die after confronting Palpatine. Rey becomes a Jedi slaying her undead Grandfather and a weakened Ben Solo has to watch as his army falls, the power he is promised is taken from him, and the one he tried connecting with dies in his arms and he can do nothing. On top of that the only people who can vouch for the good in him are dead. If he was also to become a Jedi he's also deprived of a teacher, would be distrustful of most given Palpatine, and the last Jedi knowledge is in the hands of the New Republic among the people he spent the last few years pissing off. That just sounds like a way more interesting hook to me.