Those are some interesting ideas! It's alot to soak in on one reading! LOL But I like the idea of the 5 year skip and that we lost some people and the remaining ppl have gotten a little darker. But I think if Cypher is dead, there of course needs to be a new antagonist. Maybe Cypher's son wants revenge for Ravenia killing him. 

Also, a part of me wants Sun to have died. Just an example that even something pure of heart like Sun can perish under unfortunate circumstances. 

Who was the Russian? 

And I think the person who was the catalyst, should be Shay, since if I remember correctly, Ravenia was very close to her. 

I think the Harpies, are born anew, kinda like a Phoenix. They died and have been reborn as three new harpies. I personally, would replace the Gatekeeper with a different role since in the last story, The Gatekeeper didn't really get much to do. But I think it may be a cool idea if the Paradise Lands either expanded, as you said, or moved to a new location since that location was ultimately comprised by Cypher Vale. I think some Cypher Vale's group merged with PL, like Eliza and Kaiden, but most perished in the battles. 

Or perhaps, The harpies can be replaced all together with a new role, like the 3 shapeshifters or maybe the 4 shapeshifters. They can do full or partial transformations. 1 can turn into animals, 1 can turn into other people, 1 can turn into the elements(fire, water, wind, earth, plants, electricity, ice, etc), and 1 that can turn into inanimate objects. 

Sorry, this is very jumbled. I'm just getting really excited at the idea of reviving this.