I think this would be cool to see especially given Zaytos said Zedd wasn't beyond redemption. I think a good arc would be some other old villain to return like Master Vile and for him to do something to Ollie like capture him and force the rangers to have to seek Zedd's help only to Learn Zedd has escaped and is chilling on his old thrown.

When they arrive, Zedd is shown to just be depressed and decides he's just done with everything and tells them to leave. He's shown to not even have interest in Vile's return and then the Rangers bring up Ollie and suggest he might have truly cared about him. Then Zedd gets mad and they leave and as they fight Master Vile's forces they start to lose and Vile decides to kill Ollie as some for of cruel act then Zedd shows up blasts him saving Ollie and says "I will be the one who conquers this universe!"

I just like the idea of Zedd actually caring about Ollie and I think that could be the key to his redemption. I could also see the Psycho Green Ranger returning in their era with his own new team as part of some future arc for the Cosmic Fury Rangers.