Roald Dahl's Charlie and the Chocolate Factory was a musical all along, with the lyrics to several songs right there on the page. These were pretty faithfully adapted for Tim Burton's film, but the 70's movie had plenty of good tunes of its own.
It's definitely suitable for Charlie to have big numbers in it, mixed in with all of the other delicious, sweet things. Ultimately, Charlie has to be about bright colours, big emotions, excess and joy and I can feel much the same way about a gorgeous, overblown bit of song and dance as I can a chocolate bar the size of my head.
So I'd say David Greig and Sam Mendes were off with a head start when they got to work adapting Dahl's book into a musical for the stage.
Here's the first proper trailer for the show, teasing some of the design, the original music, the one song they've held over from the 70s movie… and a suitably ridiculous, crafty approach to the Oompa Loompas.