If the 777 operation is going to be based in SYD, makes sense to put crew and maintenance there too. Whether that's a stretch for Virgin financially is a legitimate question.
Getting a deal out of state premiers is candy and baby stuff.
(Feds aren't that hard if the right unions are involved - see car industry)
V-Oz adding flights at SYD is no diff from Delta, Bloggs Airways, or even QF adding flights. It's passenger growth that will determine the speed of development of the "New SYD Airport" (my preferred option). Doesn't matter who carries the passengers.
I think the original plan for the Jet Base assumed expansion (relatively urgently) of the QF terminal. Jetstar slowed that down by using t'other terminal with Virgin. But unobstructed taxy-in, taxy-out is still an issue.
What a complicated thread!!