The reason why QF mainline is unlikely to go back to Paris (apart from the politics of slots at CDG) is that modern airline financial models favour "out and back" operations where they get two sectors out of the operating crews with only one accommodation and allowance cost. When QF mainline previously operated to Paris (& Rome etc), the operation involved each crew flying four sectors with three lots of accommodation and allowances - therefore crew costs are significantly higher. When Qantas was refused rights for a daily service, it was cheaper to code share with Air France who were flying a daily "out & back" service CDG-SIN-CDG.
Future Jetstar operations to Athens and Rome look like being flown by crews from Jetstar Australia (International) and Jetstar Asia - Jetstar Oz will do an "out & back" operation from Australian ports to SIN and Jetstar Asia will do an "out & back" operation SIN-FCO-SIN and SIN-ATH-SIN. This will result in lower crewing costs as well as giving crews more nights at home thus allowing higher utilisation. This concept is not new, eg Australian Airlines (AO) was set up to operate from Cairns to the Orient under this style of planning.
All the desire by Oz based crews to operate these trips will not cause the financial geniuses who manage airlines to deviate from this planning model. Airlines like SQ & EK etc have the advantage of being based in the middle of the major routes, thus their flying patterns are almost entirely "out & back".