And to go along with it for Part 25, you're pretty much guaranteed to be doing something "thinking outside the box" if you're doing a clean-sheet design, becaus

And to go along with it for Part 25, you're pretty much guaranteed to be doing something "thinking outside the box" if you're doing a clean-sheet design, because the current models (737 Max8, A320, etc) are all pretty darned close to their local optima. No one's going to do a clean-sheet design for 5% more pax and 5% less fuel burn, they're just going to riff on something that already has type approval so that a good chunk of the regulatory burden is already mostly taken care of.