The choices are fairly simple. Either Virgin takes on a full service component and Star Alliance membership, or a third carrier under the Silk Air (SQ) banner will be here in the near future.
Are there any developed western countries where at least two full service carriers don't compete against each other ? This is in addition to any discount carriers.
A third carrier would affect Virgin to some degree, but the competition target would largely be QF.
A lot of passengers are purely choosing Virgin as it is the only alternative to QF.
The terminal issue is interesting, but now SACL has the lot, I believe a third carrier would have to get almost guaranteed access to terminal gates.