Please don't let it be true! A replacement for the A319 could be possible. Wouldn't it be cheaper to just to rip out six seats and delete the second set of window exits and get rid of the fourth crew member. Surely the benefits of having a pretty common type would off set any fuel savings in the smaller CSeries?
The A319 could have a lower cost by a reduced MTOW, 25% less cabin crew, same type rating, virtually zero entry in to service cost, no additional training cost, no hassle associated with a new type, no issues with spare part supply and the operational complexity of split types.
EZY like to keep things simple. I hope they don't go CSeries.