B772, it could be anything. I'm only sprouting off based on the information I've read over time on Pprune. SIA wants a shot at domestic ops in Australia to add to their international services. The lack of codeshare means a cap on their growth in Australia. Qantas has an enormous advantage over every other operator into Australia because of their International and Domestic integration. As a comparitively small operator on the PER-SIN run, Skywest would be taking some big risks. The main one being that other airlines with much deeper pockets would quickly find out if they were making a profit and jump on the route. Another issue would be expanding from a domestic into the international marketplace. A tie-in with SIA would make an expansion a much safer bet. The links mentioned above in other posts with Singapore seem to be more than just coincidence. A codeshare domestic operation with SIA would be a relatively safe way to expand into trans-national domestic ops.
Perhaps I'm being overly optimistic, but it would be nice to know. I would enjoy seeing some real competition to Qantas.