This could be a goer on non premium routes, with SQ getting a high percentage of its profits from the front cabins they wouldn't make money on SIN - CNS or SIN - OOL. A B777/A330 all economy with a tighter seat pitch, run as a low cost model could be profitable.
With the growing markets of China, India and SE Asia readily accessible via Singapore it could give a welcome boost to the Australian tourist industry.
Possibly the less premium routes such as BNE and ADL could be served with a two class operation along the lines of Jetstar A330 StarClass.
4-5 hours is long enough in a narrow body, but 7-8 hours is alright in a wide body.
SIN to London could also be considered using a secondary airport such as Stansted, which feeds into the Ryanair network.
Supermarkets typically sell a home brand economy, home brand premium and regular brand version of most products in order to cover the market. Airlines seem to be doing the same, look at the three different fare options presented on the Virgin/J* websites.
Jetstarisation of Singapore Airlines perhaps ?