So, here's the premise- in the mid 11th century, a Vellalar prince, looking to gain influence and power in the Imperial Chola court, funds and organizes a small colonial expedition to search for new unclaimed lands south-east of Java, attempting to follow the spice route back to its ultimate source; first establishing a trade post on the island of Sumba in passing, but then pushing onward in a south-easterly direction, bypassing the Savu Sea, and discovering North-Western Australia in the process (making landfall somewhere along the coast of the Joseph Bonaparte Gulf).
And over the course of the next few decades, he subsequently follows the standard MO employed by the Vellalar across South India, Sri Lanka and Sumatra- wherein settlers would move in to colonize virgin land, which had previously been used by hunter-gatherer tribal peoples only for slash-and-burn agriculture and/or hunting, and convert it into prime agricultural land (with 'Vellalar' being an honorific title, granted to a select few people who would organize such raids and establish such settlements, with the chiefdoms themselves also known as 'Vel', and the title of 'Vellalar' historically being restricted to the heads of these villages, or the aristocratic lineages of their founding chiefs).
BTW, the primary narrative viewpoint (of the 1st installment in a planned fictional family saga alternate history series, drawing inspiration from the works of Edward Rutherfurd and James Michener) isn't going to be that of the aristocratic leader of the expedition himself, but instead a member of the Setti-Guttas, one of the Chola trade guilds, which was famous for specializing in the field of mercenary warfare more than actual merchant activity, with its members most often hired by traders to ensure protection of itinerant groups and caravans, as well as to ensure the safety of trading settlements.
And these pioneers focus on native sandalwood (Desert Quandong), camphor, cineole (eucalyptus oil), coral, pearls, and rudraksha prayer beads (seeds produced by tree species in the genus Elaeocarpus- with the largest and most colorful of these just so happening to be produced by trees native to NW Australia- which were deemed sacred to the god Shiva, whose temples were also established and utilized across the Chola Empire by the Trade Guilds, and effectively doubled as the Guilds' corporate headquarters) as the most lucrative commodities to exploit in establishing the first permanent colonial trade settlements.
How successful do you imagine that the Tamil Chola settlement of Northern Australia (perhaps expanding outwards to influence the entire continent as well, in later generations) could possibly be, then, without stretching the bounds of plausibility too far- for instance, in a best case scenario, could Australian kingdoms and/or empires conceivably arise which are more populous and/or powerful than those of the Indonesian archipelago, or even than Japan? And by the time the first Europeans arrive in the region, how radically different would you expect this world's Australia (or rather, 'Kumarikkandam') to be, compared to the Australia that the Europeans 'discovered' in our own historical timeline?