Off the cuff I would think a Sud Aviation SE 210 Caravelle style city to city design might be within their capability and have the most market to take. SAS could build a Southwest Airlines style service connecting cities in Europe in circuit rather than hub-and-spoke, as a neutral carrier it can cross borders, and the aircraft becomes the European 737 a generation early? Can it overfly water as a twin engine? Does it need to be bigger than Caravelle for profitability? Would it benefit from a European engine supplier, such as RR to open the British/Commonwealth market? As a sort of "regional" aircraft this design I think has potential to track into a future 737 competitor, maybe drawing SAAB into an Airbus consortium as the "smaller" aircraft specialist?