Lots of countries have. I was on one of the last flights to transit through Taiwan. Here in the UK, the government have been talking about a program to get brits back from Australia because many of the places you have to stop and refuel are closed even to transiting passengers. https://www.aljazeera.com/news/2020/03/coronavirus-travel-re... https://www.gov.uk/foreign-travel-advice/australia/return-to...
> get brits back from Australia There is/was a commercial non-stop from Perth to Heathrow, and with how many people they'd be flying, you could also use a half-filled 787.
You can (could) fly Perth to London. But will Perth put up with extra flights when (say) Singapore won't? And Western Australia has closed it's borders too, so you'll need political approval, can you get that? And are you sure you will have aircrew that will do the trip? And 26h is a long time to be on a flight, what happens if someone starts coughing harder and harder, you can't leave them at the midpoint. And remember, your airline is now on the verge of bankruptcy, so there isn't a budget for any of this and everyone senior is busy...
Interestingly they were talking about doing London-Sydney back in Jan. Popular Mechanics had an article about re-enforcing the Hull so pressure inside could be higher so you would not feel as rough at such a long flight...