457 Visa or not they will still have to live somewhere. Only in Aviation would there be a company stupid enough to move a maintenance base to a town where there is difficulty getting accommodation and ridiculous living costs.
Do you think Rio/Woodside/BHP base people up there by choice?
On saying all that I wouldn't be surprised if this is the first move to try and get away from Perth Airport. If they isolate Perth Int'l to just a backwater regional airport and expand KTA and PHE with 767's doing direct everywhere it might be a good plan.
Good opportunity for the KTA airport and council to setup a nice little hub airport for themselves if they do it properly. Any news on a terminal expansion? A Customs hall by any chance? It's pretty obvious that Perth Int'l have no interest in running a decent facility.