Having seen several people on this forum and elsewhere online swear by this plan, I was intrigued by the possibility of adapting it for passenger operations.
Dissecting the original plan
The basic genius of the GG&N is that it can function as either a double-track figure eight or a folded dogbone, and that it does this without complex reversing loops. Since a straight doubletrack figure-8 looks toylike, the tracks on the lower level are broken apart.
Converting to passenger
The lower-level trackwork on the original GG&N comes close to approximating a four-track station and adjacent coach yard, so this makes a natural starting point. Flipping the levels makes the station and yard the centerpiece of the layout. The foreground "reverse loop" on the original GG&N has a crossover on the left-hand side of the layout, then a simple switch on the right. Flipping this so the crossover is on the right "cleans up" the left side of the layout, which allows for an additional, shorter passenger station with its own passing siding. From a modeling perspective, you'd probably want to give the appearance that these are (or were) stations of two competing railways, with different ballast coloration and station architecture.
After that, I managed to work in most of the spurs from the original GG&N, although to be honest I'm not sure what you'd use short spurs for on a passenger road. Perhaps there's a couple of holdout freight customers who still get served by a nightly switcher run, or perhaps one is a RIP track. At the very least they'd make a decent place to park a Deltic or an EF63.
The original GG&N was designed for a 5x9, in HO. Most N scale adaptations I've seen shrink this to 4x8 or 4x7, which still requires a "table" with access on both sides. In this plan I "squashed" it to a 3x8 with a peninsula on one end, designed to fit into the corner of a room. The large station platform is designed to hold 8-car EMUs or DMUs of British or Japanese outline (max. length 20m). The small station will hold 4 cars, although there's enough room to stretch that to 6 cars if you so desire. Minimum radius is 12.5" throughout, track centers are 1.25", and turnouts are minimum Peco Code 80 Medium.
GG&N, Suburban Division
The original GG&N: