CaptJCool, thank you for the intellectual challenge of pondering this
I will have my own stab at it, and include reasoning just to be fair (as I have a late night crystal ball that is unfailing, so makes the contest a tad unfair to others
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You were not specific in stating from/to regions, so I am assuming the question is from Australia to those other regions? And I also understand your question to mean "when will international travel not require an isolation period upon arrival" - as this is clearly something that mainstream tourism and most business travel cannot take. In any case I will answer your question in two parts - the first as to when areas will open their doors to international travel. The second part will be from the Australian end.....
Asia
This will be a very staggered affair. Countries such as Indonesia and Vietnam will open their doors very quickly - perhaps in about four months after the tsunami has started to ease - so call it from late July onwards. At the other end of the spectrum is China - they are a powder-keg that needs to stay sealed until a cure or vaccine is invented and implemented - so count China out until at least March 2021. More likely July 2021.
America
They are different from the impoverished asian nations in that tourism is not such a high priority. But through either ineptitude or cold economic planning they will also have the curve peak very soon - so I expect that international arrivals will be welcome possibly around September - their curve will have peaked before that but they will take a few extra months to get over the mass burials and again accept that the economy is yet again their number one concern.
Europe
Like asia, a mix of very different kettles of fish, but also somewhat similar - they will undergo their carnage over the next two or more months, but will rapidly then desire to get the economy moving again - so as a broad prediction, again I say September 2020 as per USA. In the next week or two some countries may be more succesful/aggressive in slowing the curve so they may hold out until end of 2020.
Middle East
OMG. Has anyone EVER predicted something in the middle east with confidence?? I would expect overall that the drive to renew tourism will vanquish any real decent reasons for any decision. A most disconcerting region where common sense is very absent - or at least we as westerners cannot fathom the whole deal. I predict the principle nations (travel wise) such as the UAE to be opening for business very soon - maybe as early as July 2020.
Pacific
Yet again, a complicated region. So very much dependant on travellers and tourism, but also wealthy enough in spots to adhere to best practice. Take for example Rarotonga - lives from tourism, but has a very elderly population and scant medical services. They will truly struggle in making decisions. I think (hope?) that they are a society that values elders lives more than economic success - hence I think they will keep their borders closed much until, like China, a vaccine or great cure is found. So Let me guess that in general, opening to tourism, etc will not occur till mid 2021.
So now to part two, which really is the big one: What will Australia do? I think that although we will suffer, we will be more succesful than many other countries in lockdowns and flattening of the curve. At the moment there is much focus on the economic side, but once the wave really hits us the tide will turn somewhat to the other side - that of sheer deaths and human loss. I think we will be in some sort of lockdown for a very long time. So even if other countries open their borders, we will still have restrictions (such as upon-return enforced isolation) that wil make flippant international travel very unappealing. I am here probably going to go way out there, but I predict we as Australia will have severe travel restrictions for about a year. So March 2021. Unless off course some miracle cure/vaccine appears before then.
I personally have given up on contemplating any international travel until about that time - March 2021.
This is going to be a memorable and long year for us FF addicts
