Good idea i'd like to see with a patch, but not as a FULL expansion. But to be honest Northrend is a good enough area for levelling there's a lot of variety in the different zones which keeps levelling phone. having the same repetitive mobs and ish would make it boring /cough cataclysm.
Anyway they should hire you in an instant. You got a great brain that just needs heading in the right direction as well as amazing art skills. You should consider applying!