By the 4th quarter of this calendar year both the US and UK, as well as Singapore, will be fully vaccinated. Consequently there will be negligible cases if any. Their borders will be open and unrestricted. The yanks are doing that even now for those vaccinated!
What will Australia do then?
Little if any cases here and over there. Significant numbers of Australians vaccinated. The elderly and vulnerable fully vaccinated.
There will be little logic to argue against travel to these countries.
What little logic exists will result in, at the very least, an arrangement like the Tasman Bubble.