no, NW should not
747-200's are getting expensive to operate and maintain, and are more suited to longer sectors, certainly more than any NW domestic route.
Secondly, NW does not need an a/c of 747 capacity for its domestic services.
As stated, the 757-300s will assume the highest density routes when they join the fleet, supplemented later, when neccessary, by the A330s.
How many A330s are NW to recieve? all 300s? any 200s?