Maybe they'll get Kiske to sing parts of King For Thousand Years, Occasion Avenue, and My Life For One More Day in order to create some real finality too the Keepers saga.
I was thinking too about Kiske having a go with King for a Thousand Years! Even though the lyrics are entirely from the point of view of the devil from start to finish so it would be weird to have two different people singing it.
I wonder how they'll approach the show, the press release say it will be nearly three hours - will they do a mini-Avantasia with Kiske and Deris coming and going, or it's gonna be the Deris set, the Kiske set and then the inevitable duets in the encore? there are many combinations, and I hope both Halloween and Keeper of the Seven Keys will make the set. Also some love for the other Kiske albums would be nice, Kids of the Century and Giants could be two realistic choices.
EDIT: another thought... not even Iron Maiden announced one year before their reunion tour, they got back together in February 1999 and in spring they were already on tour, summer at the latest. They've announced NOW the first date in OCTOBER 2017, 11 months away, what are they gonna do until then? does Kai Hansen have a new Gamma Ray album and tour already planned? until October 2017 there's time for writing, recording and releasing with the proper promotion a new studio album, it feels anticlimatic however to have Helloween have just another studio album and then go on tour with Kiske... I hope for more details in the future!