Hmmm. Miles this was discussed a few days ago and I said at the time that people should discuss this with a tax specialist, I am just a layman.
My layman's understanding is that you need not live in it, you can live or rent elsewhere. I am happy to be directed to the appropriate area of the ATO website. I had trouble finding it when I last searched.
I know you are tax specialist so I am very interested in what you have said.
I believe that historically it was introduced to allow military staff to have a CGT free home even though they were always renting elsewhere.
I think it is worth following up if a person is in a position to use the ruling, they just need to see if it applies to their particular situation.