The CS300 has the ability to kill the A319. QR have just recently announced that they are ditching the A319NEO in favour of the 320/321. I think they may just ink a deal for C series sometime in the future. The issue with the C series is bombardiers credibility due to the fact that it is their first foray into a project of this size, at least that's how it's being perceived and played out in the media. Added to this is the fact that there isn't a huge backlog of orders so no one is in a rush to book slots.