The Myair.com order for the CRJ1000 was originally an order for 19 x CRJ900's, but stated that if Bombardier went ahead with the CRJ900X aircraft that they would convert 15 aircraft to the larger aircraft. I don't think that you'll see a Northwest order converted to the larger CRJ1000. Most U.S. carriers have really strict scope clasue restriction and I don't think that Northwest (or any other mainline carrier) would want to fly the 100-seater from Bombardier. This is not true with US Airways as they operate and have ordered a number of EMB-190 on mainline routes, but I don't think you'll see Bombardier being able to do that as well.
I believe the thinking of executives at Bombardier was that they were focusing this aircraft at the European market and that's where the orders have come from so far.
I also believe that the CRJ1000 is more expensive than the EMB-190, but I am sure others could give you a better Idea of initial costs, maintenance costs and fuel consumption, etc.
Some stats from BBD: http://www.bombardier.com/CRJ/en/eco...omics_crj.jsp?langId=en&crjId=1000
Just my two cents,