I got to play JJPPOTC about 20 times at expo and love the game and where it's going. I think it would be really cool if you can collect the other characters and their special abilities as you play. Seeing how there are 20 or so of them and more than likely a few will stand out as the ones you will want to pick in the beginning, it would be cool if you could utilize more of the others as you progress through the game. Maybe it's a random character awarded at different gold collection levels, maybe you earn a character after completing a chapter, etc. Maybe the number of characters you have entering a multiball changes your ball save timer or number of balls in play. You chould have a really deep wizard level mode after collecting all of them! Everyone likes carving their initials on a game and a Character Champion could be a cool objective.
Also, I know the chapters were preliminary at Expo, but it might be useful to think about using the larger triangular inserts as more of an integral part in the chapter shots. I'm used to games when in modes/chapters using the largest inserts to guide the important mode shots. It was tricky sometimes locating the smaller flashing inserts to know which ones were key for the chapter I was in.
Just my $0.02. Game looks fantastic and may be the first JJP game in my collection.