Does Boeing close up shop? Build the 818 or the 7107? Follow Microsoft and build the BoeingME, Boeing XP, and Boeing Vista? (I assume they’d skip Boeing Bob.)
The Y1 is slated to replace the 737 family, the Y2 (aka the 787 Dreamliner) will replace the 767, and the Y3 will replace the 747 and 777 lines.
Close, but more likely 7F7 or 7G7 if they keep that naming pattern - the development name for the 787 Dreamliner was the 7E7.