I do tend to agree with the "Who would the Chinese conquer" question in this regard.
However, I can think of one example, a significant one that would make a maritime China disgustingly wealthy (and protect them long-term)
Indonesia. Control of the Spice Trade, the Straits of Malacca, its food, its taxable wealth - its the only region besides India that could compare to China.
If you have that conquered and engage in settlement, it then opens up the door to settlement across the Indian Ocean (i.e. small trader colonies), but also in Australia.
When Zheng He died an outside observer would have every reason to expect that to happen. There were large numbers of Chinese in Indonesia then, Palembang had a Muslim Chinese ruler. A number of Zheng He’s Muslim crew got jobs supporting Muslim rulers in Java. After the Ming lost interest however the Chinese traders left and didn’t return until the late 16th century when the Chinese diaspora really started to grow.
It’s curious why the treasure fleet never looked to taxing trade or controlling spices to fund their operations. Perhaps their leaders were bureaucrats with no mind for commerce. Still it seems to me had the Ming maintained a presence in the Indies a generation longer, the wave of arriving traders would make this very likely.