If a flight attendant told me that I couldn’t bring my roller bag onto the plane, I might throw a fit. But when the same idea comes from Teague—the preeminent air travel design studio that’s designed the interiors of Boeing planes since 1946—I’ll hear them out. Recently at the Airline Passenger Experience Association (APEX) conference, Teague principal brand strategist Devin Liddell presented the company’s radical concept for Poppi, an idealized, modern airline. “Our scenario was,…