I think the big advantage SLC-SYD has over JNB-ATL is the density altitude equation in the winter. Very likely this would be a northern hemisphere winter seasonal route. That time of year the DA in SLC shouldn’t be too limiting unlike JNB where the same time of year it’s hot.

I am curious to see as SLC continues to expand if it sees more international. It seems like it’s the best west coast airport for expansion and it already supports quite a bit of connecting traffic.