You are thinking along the same lines as me monalith99, but my guess is Mystic Prophecy. They don't have Gus G. any more, but judging from what I've heard of their upcoming disc he isn't missed all that much .. if at all.
MP is an under the radar type I think, but they are of the highest quality when it comes to Power Metal, and play at an energy level that will blow the roof off the house.
I don't think they would normally be a true headline status band, but this year I think they are because of certain circumstances, and I think they would go over very well. They seem to meet all the criteria that has been layed out.
They have a new disc coming out later this month (their 4th), and it's a face ripper. I just think they are one of those bands that would steal the show, and come out of Prog Power with a huge bunch of new fans.
Oh well, that's my guess anyway !! Even if it's not them I think they would make for a terrific Prog Power band in the near future.
Britt