The A319s are not efficient airplanes - high CASMs. No doubt there are plenty of current or potential routes (including current A319 routes) that could be profitably served by E2s/CSeries. The questions for me seem to revolve around cost per airplane (volume deal) and introduction timing.

Although I am a big fan of the CSeries/A220 and I am not surprised JB and the proposed airline Moxy have selected it for their growth plans, Embraer and Boeing appear more desperate for a deal - so, the E2 seems more likely since it is probably available in large quantities sooner (no big orders yet). Guess we will see what happens... What we can’t ignore is that there are plenty of underserved markets out there that Spirit could serve with the right airplane and economics.