I'm wondering if there's any sign that I'll ever be able to use/earn FC miles on either V Australia or Virgin America?
Who knows?
I am not familiar with the VAustralia set-up, but Virgin America had to jump through lots of hoops to show that they were an independent set up from Virgin Atlantic, in order to get permission to fly in the first place.
Since they started, we have seen a little bit of co-operation (VX pax in VS Clubhouses for example). It could be that there will be more coming together in the future.
VX have their own EleVAte programme, and I am not aware of anything other than rumours of FC earning on VX flights in the future.
Nick