Last year Delta was looking at replacing its older, smaller airplanes with either something from Embraer or 
Bombardier. Then in an interesting turn of events the airline decided to put that on hold and ordered 737-900NGs. This was followed by an even more interesting decision to take over the AirTran 717s. It seemed the airline was done with its requirements on the smaller sizes – especially after went on a shopping spree to acquire more MD90s.
Today Delta announced it is replacing its CRJ200 with CRJ900s. Delta will acquire 40 new CRJ900 two-class regional jets, with the option for an additional 30 CRJ900 aircraft, and Bombardier will assist Delta in phasing out 60 single-class CRJ200 aircraft.  The 76-seat CRJ900 will replace less efficient 50-seat aircraft on a capacity-neutral basis. Retiring these aircraft reduces fuel and maintenance expense, improving Delta’s cost structure and environmental profile.
Of course this is excellent news for Bombardier. But it is a blow for Embraer. With Bombardier in at Delta, it opens the airline and OEM for evaluations of the upcoming CSeries. On the other hand Delta has made it clear they are not swayed by new airplanes – recent fleet decisions demonstrate this.
That said, Delta has a complex fleet with a lot of crossover in the 737 and A320. They need to seek fleet simplification to keep MRO costs down. The older fleet requires more MRO expenses even if the capex cost is low.
I think NWAC and now DL management are highly regarded for costs consious, often unconventional fleet management. This must be a major boost for BBD.