I believe I understood the question, which means that it was my answer that was not clear, and not your question!
If you’re in Engrave Mode and you switch to Setup mode, it should display exactly the same thing — say, page 6. I would have to test as I can’t recall this behavior from memory, but I think it should to that even if you were in Galley View in Write mode before. Might be wrong, but I think it should be like this.
Either way, Daniel has said that he’s considering implementing a quick preview shortcut.