Bravo Delta
It might surprise you to know the following airports, all of which have scheduled flights serving them involve IFR flight outside controlled airspace, day or night.
Kaitaia, Kerikeri, Whangarei, Whakatane, Taupo, Wanganui, Paraparaumu, Hokitika, Westport, Timaru. Later at night you can add Hamilton, Palmerston North, Napier Gisborne, New Plymouth, Tauranga, Rotorua plus a few others.
As utopian as your suggestion is I don't see radar control services being provided in these areas either during main business hours far less 24/7. The cost is too high. From what I am observing Airways cannot staff their current requirements without them providing even greater coverage.
Also are you telling me everywhere in Oz has radar services in similar areas?