Revue ideas for old & new theme

The R&H Goes Pop series on Youtube could be a good place to start, as they're pop versions of classic Rodgers and Hammerstein songs. And if you have someone who may be good at composing/arranging pieces, you can try to do a mash up of some songs that could play off each other nicely. Or similar to your idea, you could showcase different musicals that touch on the same subject matter, like 1776 and Hamilton, or how a genre has evolved, like rock musicals with Hair/Jesus Christ Superstar and Spring Awakening/Next to Normal or even jukebox musicals like Crazy For You and Jagged Little Pill/Head Over Heels. Stuff written by the same composers who've had long careers like Andrew Lloyd Webber or Stephen Sondheim could also form a different segment.