Turns out the RVP this year is actually taking place at the Palladium, which of course is where Wizard of Oz is opening in Feb / March. Sister Act finishes this Saturday, then they've got about five weeks during which lots of building work is taking place, the Sister Act stage is coming out and the Wizard of Oz one is going in, just in time for the RVP, then they'll have it all set for rehearsals until Oz opens.
So since it's his theatre and the stage and set for the RVP will largely have to fit around the Wizard of Oz plans, I guess it's no surprise that Oz will feature in the RVP.