I believe to renounce you must first have dual nationality. You could marry a foreigner for nationality, then (eventually) both renounce your home country.

While that is the smart way to go. The USA is one of the few country's that will allow you to become stateless.[1] But I am not sure why you would ever do that.

[1] https://en.wikipedia.org/wiki/Renunciation_of_citizenship#St...

Not exchanged, but considering Australia and America are both immigrant countries, you may be able to get an Italian or Irish passport based on ancestry if your ancestors came from there.

I always wanted to start a "couchsurfing for passports" , or even airbnb. If one is a citizen, they can vet for an exchange citizen, sounds democratic to me.