To say that Singapore will become irrelevant because of longer range aircraft shows an ignorance of the market which SIA, and to a lesser extent Qantas, serves. Changi operates as a hub, and one visit to the airport will make it obvious that it is set up for a smooth flow of pax from one flight to another - much more so than most other airports anywhere around the region. An example is the same-level arivals and departures with no requirement for transfersbetween floors as is the case in somewhere like HK. They feed pax from destinations such as India through to the US, Australia, Europe to Asia. Their great advantage is their central location where they can be hub and spoke, not like a largely end to end carrier like Qantas. This is not a defense of SIA, simply an observation.
The fact that Singapore is Qantas' second biggest international hub outside of Sydney says that they also see the advantage of the place. They don't hub from Darwin to Australian ports, or Perth or Cairns but Singapore.
Also, for all SIA's faults, they know their product and rarely take their eye off the ball when it comes to the customer, something which Qantas can't claim (Jetstar being a prime example). If Qantas have not served their customer's well on the Pacific then they deserve the competition. They will not relish competing with this particular carrier though.