I wonder what F on the upper deck would look like, just hypothetically.

One option would be to have 2+2 like Lufty, but this would I think be unsatisfactory.

Maybe they could have a reverse herringbone configuration, with each seat facing at an angle between facing directly forward and directly towards the fuselage. There would then be a small 'corridor' so that the passenger could get to their seat and a storage shelf, locker and dividing partition on the other side of the seat. Take out the lockers adjacent to the fuselage and you could get quite a long seat in there.