IMO, if the Q400 was ever introduced, it would be to replace the CRJ200 and to upgage some saab routes. The Q400 i stoo big for a direct saab replacement, but a mix of Qs could do the trick, or even a mix of the ATR family. Yes, it would be introducing a new type, but we would eventually see the saab go away. If the fleet size is large enough, the economies of scale would justify adding a fleet type.