Actually the NZ to Oz rally
been tossed around before... in the late 90's some colleagues and my old man etc. looked at the logistics/possibility of running an ANZAC Safari... there were breweries and government's etc. that were keen to back the idea...
The South Island of NZ has some great expanses of mountain terrain with which to conduct (Andorra like) cross rallye stages up to a couple hundred km'sin length.
The main "hitch" with the NZ idea was; the relatively long boat/ferry transfer from Auklund/Wellington to Oz; it's not an overnight proposition - as is the case with a Mediterranean transfer - like were part of the African Dakars of the past... It is more like a three day proposition (at best); which was deemed to be too great an interruption to the rally's continuity (couple that with the Australian Customs reputation for cleanliness regarding imported vehicles; consider that the first three legs of the rally were to be run over the sheep shit encusted mountains of the Kiwi's Sewth Eyeland... then legs 4, 5 & 6 were shaping up to be a World Championship on board car washing tournament
... all was filed in the "too hard" basket.
Even before that (in 1993) my father was retained by Thommy Sahato and the Indonesian government to set a rally that extended the Safari (it's annual pilgrimage back then, was 6500 km's Sydney to Darwin) from 9 stages in Australia (with a ferry link via two huge car/passenger ferries with accomodation) across the Indonesian archepelago via the Islands of Flores, Sumbawa, Bali and Java (5 stages), to finish in the Indonesian capital of Jakarta. It was a pretty cool concept... the "Bivouac" was to be onboard the car deck of the ferries each evening (accomodation in the upper deck cabins) as the boats cruised from one island to the next.
All the suryeys had been done, the course was set, the money appropriated from both the Aussie and Indonesian govt' etc. and all was in place for the innaugural Sydney - Jakarta Marathon Rally in 1994... But the island of Flores was hit by an earthquake/tsunami in late 1993... caused a national disaster/state of emergency, and the event was postponed/cancelled.
The subsequent 1994 FIA World Cup Australian Safari (Syndey - Darwin 6,500 km) was in fact the first nine days of what would have been the 14 day Sydney-Jakarta marathon. Unfortunately, by the time the 1995 event planning was to be put in gear, there had been a change in the indonesian gov't/infrastructure and the idea was shelved/burried... never to be.
So, as (another long) answer to your question... yeah sure; the Australasian region is more than capable/suitable to conduct a DAKAR (length) rally... it's just a case (as always) of the money and political aspects being put in place... In Oz the political part of the equation is more than achievable... but as is so often the case, it is the matter of money (and where it comes from/pays the bill) that is the crucial part.
There are undoubtedly places all over this globe that would be awesome to conduct a marathon rallye raid event... as the posts in this thread (and various others) are testimony to... The one BIG thing that sets the Dakar apart from other "evets/organisation" in the sport; is that ASO has found a way to reconcile the commercial pipedream, with the logistical realities and the PR/marketing image... and produce this spectacle year after year.
And for the last four years (since the 2008 incident), I reckon they've done a damned fine job of it too... all things considered