The A319 and 737-700 are smaller versions of much larger designs and structurally, they carry the weight and shape of every part that does not get scaled down. They are also designs with roots in the 1960's.

The C-Series brings to the table new structures, wing, tail and engine technologies. It is thus far very expensive and Bombarider is doing little in the way of incentives to get it sold.

Boeing and Airbus have amortized the cost of A320 and 737 development. Their factories are uber-efficient. They've been beating Bombardier on price and service. Also, the 737 is very inexpensive to maintain from a spares and rotables perspective.

The MD88, for all the crap I throw at it, is a remarkably efficient airplane. It's probably holds it's own against a new'ish 737 on routes less than 2 hours in duration.

IMHO, the airplane that is uncomfortably above the curve is the 717. There might be enough of a savings there to cover the C Series purchase price ... .

My guess, eventually, 787-900 and CS-300. Richard Anderson (and his team) are smart to want the stretched version (not the double shrink). But, he has no reason to get in any hurry. The MD88's doing fine and the 717 fills the gap. He wants to see someone else take on the risk of launching the new Bombardier type.

Of course, if Bombardier takes RJ's in trade for big discounts .... anything could happen.