He is a dual national now, which only complicates any attempt, Australia's connection with Five-eyes and other military and political arrangements aside.
By your host country maybe (though I don't agree it's as cut-and-dry as that), but your home country will still treat you as a citizen regardless of your other citizenship statuses (except in the case you are a citizen of your host country). So they should still give you the same aid they'd give any other citizen -- and in some cases the UK has actually helped UK citizens flee a country even though they are a citizen of said country (examples include forced marriages of dual Iran/UK citizens in Iran).
Care to elaborate? What kind of benefits one could get out of it? There's tons of information on topic from biased sources like law firms, but very little otherwise.
In many countries you can't have two. But as long as "dual citizenship" is recognized, there is no upper limit.
Older people probably value choosing favourable healthcare systems too. Nations aren't static entities, I'd doubt you'd find many people willing to bet on a single country's circumstance being exactly the same 30 years from now.
For the wealthy gaining dual/multi citizenship is common across the world and plenty of Western nations sell it off willingly.
https://www.scmp.com/news/world/united-states-canada/article...