As for QF getting the A340-600, SQ has spoken quietly into QF's ear about their hassles with the longest range A340 which are numerous.
Anyone wanting to challenge this go right ahead - SQ has no long term plans to have this aircraft in their fleet whatsoever and are keen to see it go in favour of the new B777.
Long term plans at SQ call for A380's and B777's only.
QF can have a mix of A380's, B744's, B777's and B787's to replace both the B737's and B767's longer term.