Southwest can't be crushed, it's business model is too well protected and strictly followed.
They are also very big now, one can't start operating a fleet of 10, let alone 30 or so A330-200/300's in Asia, that would require one massive bankroll. WN has several hundred B737's.
If someone started an airline that flew HKG-SIN, and started with say 2 A330's, then it would be swamped by the 4 and 5 dailiy flights that CX and SIN operate each (and add QF, UA etc. into that mix as well). It wouldn't attract any business traffic, and it would be hard to operate an A330-300 with about 350-380 pax and be profitable only offering low fares over such relatively short distances as HKG-SIN. CX and SQ could easily lower their fares in economy, and still charge their high fares for business and first class. Cargo in the A330's, B777's etc. would easily overcome the losses that putting extra cheap tickets on the HKG-SIN route would incur. It wouldn't take long for the new entrant to fold, otherwise, someone would have done it by now. To compete, the airline would need to attack routes where companies aren't so well entrenched.
M88, 722, 732, 733, 734, 73G, 73H, 742, 743, 744, 752, 762, 763, 772, 773, 77W, 320, 332, 333, 345, 388, DH8, SF3 - want