Remember Stern makes multiple titles. Not every title has to "draw in a younger crowd". There are already plenty of younger crowd Stern machines available new and used. Avengers, X-Men, Transformers, Shrek, Spider-Man, etc. If/when Kiss goes into production, there will probably also be a "family" title on the line as well. If they do make a Kiss machine, it's to sell it to Kiss fans....just like Metallica sold to Metallica fans. If the game is good, it'll sell to non-fans on its own merits....and, as AC/DC and Metallica have proven - "music experts and snobs" have no bearing on whether these games appeal to people or not. No one cared that Bon Scott wasn't featured on AC/DC. No one cared that Cliff wasn't featured on Met. No one will care which version of Kiss is featured in Kiss. Kiss fans will be interested & buy it. Plenty of people actually like Kiss' music.
The best "younger crowd" theme would be Adventure Time ...iron is still hot & teens/adults love it too! Big animated movies that appeal to kids/adults would be good, too - Despicable Me, Cloudy With A Chance of Meatballs, something by Pixar (Toy Story, Incredibles, etc)