There was an interview with Block in today's Washington Post. Here are a couple of paragraphs that hint at the concept for this production:
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Q: How else might this staging differ from past productions?
A: Even though our central figure is Norma Desmond, “Sunset Boulevard” is from the point of view of Joe Gillis, a young, White, cis male in his 20s. So how might that storytelling change if it was shifted a bit? What if it wasn’t from the point of view of Joe but perhaps from a female point of view? With Andrew Lloyd Webber’s approval, we’re taking a different tilt into the storytelling without having to change a lot of the text — actually, any of the text or the score.
Q: Can you tell me a little more about that?
A: I cannot! [Laughs] You’re going to have to see it. But I can give you a hint: Because the narration reads very much like a screenplay, and both [Joe] and Betty, who is our female ingenue, are screenplay writers, that’s enough of a hint to let you know how this is being propelled at the very beginning.