That is a viable suggestion you make here about an early, fast, trajectory along a narrow pathway; and indeed a coastal route would fit. Aside from access down the Nile and along the Mediterranean coasts into Eurasia, the most obvious route of expansion was a coastal ecosystem highway (“narrow” despite being a wider during periods of glacial advance, when sea levels were 70-120 feet lower).
We are probably looking for a single culture group who spoke a single language. It appears to have represented only one of a semi-continuous chain of coastal demes/culture/language groups located in refuge areas along the Eastern and Southern African seacoasts during periods of extreme drought from 134 ka. to 74 ka. Afterward, the bulk of humanity could expand inland as rivers began to run and lakes refilled - and probably constituted 9-10 times the number that trickled into Eurasia.
New evidence has come to light that tells of some profound challenges that were faced by early modern humans in Africa during their first 100,000 years, challenges that only began permit the full re-occupation of the interior since about 72,000 years ago.
This data comes from climatic interpretation of deep core samples drilled in deep Lake Malawi bottom sediments. Severe interior droughts happened in four huge waves from 134,000 to 74,000. In the paper reporting these findings, these were referred to as “Mega-droughts”. which suggests the coasts were refuge areas for the species Homo sapiens during a span of nearly 80,000 years.
Each humid period during this time was followed by these severe droughts. This Malawi core data lists humid periods in East Africa at 1)148 and 132 ka, 2) 124-110 ka, 3) 85-76 ka, and 4) 70-65ka.
As each mega-drought ended and a wetter climate began, these population in these refuge areas would have experienced accelerated rates of population growth and expansion. Until the final drought ended around 70,000 years ago, each expansion into interior regions would have been knocked back as soon as the next five, ten or even 20 years of Mega-drought set in. But, through wet and the dry millennia, if their numbers were going up, the only place people could go and persist, was up and down the coast, or, possibly, north along the Nile.
It seems likely that at least some of these cultures made boats, hunted fish at sea, were intimate with fish, marine mammals, seabirds, island-hopping, and tidal dynamics; a kind of culture where people grew up with knowledge of both fresh and salt water, use of both hunting bows and harpoons, ate shellfish and fish but sought mammalian skins for clothing and blankets. This culture was capable of using three ecological areas - 1) the seacoast and 2) marine areas just off shore, and 3) the mixed savanna and forests long rivers perhaps as much as a hundred miles inland from the coast. It seems likely then, that these people were, in fact the keepers of encyclopedic knowledge about three different ecosystems - the shore, the sea and the land, and they used them all.
A culture adapted to this triple ecosystem might well have expanded preferentially along coastal environments. It is roughly 20,000 km along the coastline from the northeast coast of Africa to the north coast of Australia.
Assuming 1) a “starter” language group/deme of 1000 people, living along the coast of SE Africa, and assuming - based on my own Kalahari data - that such a group requires a territorial range of roughy 120 x 120 km and 2) an average population growth rate of .05%/year, thus a doubling time of about 1400 years*, it would take such a population, just over 12,000 years to reach the area of these Chinese sites you mentioned. They might even make it there faster, if their birth rate went up even enough to bring population growth to ~.08% a year. Another 5000 years would get them to Australia. What the new Australian date tells us is that this steady expansion along a coastal route likely started before 70 ka. But this does not mean that most of the people who undertook this expansion were not part of a relatively small genetic founder group.
*Doubling time is calculated by the formula: Td = log(2) / log(1 + r) Where: Td = doubling time and r = a constant growth rate.