No, its not smart to put a new and expensive aircraft on a long and thin route. It locks these planes up for significant blocks of time and when you have to pay off the price of these aircraft, you need high utilization and profitable routes. It makes sense for Delta to put the A319 on these long and thin routes since that aircraft is already paid off for and can be blocked out on these long routes. There is a reason routes like SEA-IND/RDU/MKE/MSY/etc or SLC-BNA/STL/PIT/etc are operating with the A319. Given that DL is getting a big discount on the CSeries by using them on shorter routes, yes, it makes sense to use the A319 for longer routes instead of a CSeries. The CSeries will be a great cost reducer on frequent/shuttle routes on large RJ/B717's like LAX-SFO/SEA, NYC-ORD/DCA/BOS, CVG/RDU-LGA, etc. That gives a lot of fuel savings and increased efficiency.

It is possible that a few long routes emerge, but expect these to be anomalies, not the normal usage of the aircraft. These will be routes where Delta can command a premium based on O&D pax.