There are three factors that will determine where NWA places additional -900s. Cheap feed, building the value of the carrier's it owns, and cost of operating a -900 vs a -200.

NWA has never appeared concerned about spreading the fleet out. NWA wants the cheapest airlink feed possible, and that means keeping an entire fleet with one Airlink carrier. All the Avros all went to XJ. The first 139 -200's went to 9E. Then XJ was awarded some -200's, but after NWA went into chapter 11, all of the -200 flying was supposed to go back to 9E. Even all the Saab flying was shifted to one airlink carrier.

Now that NWA owns XJ, some of the 9E -200 flying is shifting to XJ. This only makes sense because NWA wants to build up the value of the Airlink that it owns. Until a few years ago, 9E was owned by NWA. NWA learned that they could buy a small mom and pop airline, build up it's value by awarding it lots of RJ's, and then sell it at a huge profit. Now they are doing it again. Since the only real value a regional has is it's contract with a major, NWA will build up XJ and then sell it off for another nice profit. Ditto for Compass. The last thing I would expect would be a XJ/Compass merger, since keeping them separate would mean two trips to the bank for NWA.

The only hope I see for 9E getting -900's in NW colors is the cost of operating -900's vs -200's. Its my understanding that the -900's are nearly as cheap to operate as a -200, and they have premium seats that business travelers love. Since NW is in bed with 9E for the next 10 years, they might as well get the most out of the deal.