Except there's only really one stable coalition in Australia, and that's the coalition between the Liberal Party and some state divisions of the National Party (the Nationals in SA and WA, for example, are not part of the Coalition). The Lib/Nat Coalition has lasted so long that they are treated by the public as if they're one party, and indeed in Queensland and the NT they've merged. It's not a good example of political coalitions in general.

In recent years, there have been Labor-Greens and Labor-Nationals coalitions at a state/territory level, and of course the Gillard minority government federally, but they aren't stable - they last for as long as Labor can't form a majority government.

(Instant runoff voting doesn't necessarily tend towards formation of multi-party systems, it merely removes the risk of three-cornered contests that comes with FPTP (which is still a significant improvement for the chances of minor parties, obviously). The electoral system factors that really determine how multipartisan a political system is are whether you use proportional representation vs majoritarian (see Duverger's Law), and within PR systems, district magnitude. Proportional representation is the reason that in Australia you regularly see minority/coalition governments in the ACT and Tasmania but much more rarely elsewhere, and we see plenty of minor parties in upper houses rather than lower houses.)