Here are the songs that I consider, for each singer, the big absence from the last tour and that might quite well be considered for the next one:
Hansen - Victim of Fate
Kiske - Twilight of the Gods
Deris - Where the Rain Grows
More generally, the Deris albums are so full of great and forgotten songs that you could make an entire setlist out of them.
And yes, King for a 1000 Years definitively needs to be played, lyrics wise it's entirely told from the point of view of the devil so there's not much room to add different singers as voices but what the hell, it's not gonna be weird if different singers sing the same character, it's something you can easily overlook. for example Kiske can do the kinda happy chorus, while Deris keeps the intro and the verses and Hansen does the "we're the king for a 1000 years" menacing part.