Though the Qing Dynasty did want to leave Taiwan alone originally and only conquered it due to the necessity of stamping down on the island to render it useless as a staging point for Pro-Ming enemies, Taiwan was not 'ignored' under Qing rule. Far from it. Even inland major Chinese Viceroyalties like Shaangan or Sichuan didn't receive the amount of money, supplies and importance the Qing attached to Taiwan. The Shufan and Guiha Prefectures managed to maintain peace between the chinese and aborigines after the 1787 Rebellion and Taiwan was considered a remarkably stable province - untouched by the chaos on the mainland as such making it one of the richer provinces - until the Mudan Incident, and even then, it was both the chinese settlers and aborigines who fought back against Japan raising the Qing banners when the local Qing garrison was outnumbered and forced to retreat. From 1874 - 1895, Taiwan was basically a military fort given an island and the Qing fortifications, bunkers and layouts were the reason why Japan took around 8 years to pacify Taiwan in the end.
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As for the question, the only two options I can really see are Sri Lanka and Northern Philippines. When Kotte was conquered by Zheng He 1411, there was a huge chance that the pretenders that Ming wanted to back would be killed, but thankfully they were not and they were instead installed as pro-Chinese puppets, however due to the fear that their favored pretenders and their children would be killed off by their enemy pretenders, Zheng He had sent word to the Yongle Emperor to think about appointing a Chinese Prefect and/or Governor to the Kotte Kingdom, which in essentiality meant Annexation. Of course how long a hypothetical rule of China over Sri Lanka would last is entirely upon the butterflies that would be unleashed after such an event, but nevertheless, it would certainly be interesting.
The second of course is Northern Philippines. IOTL, the Ming Navy routinely set out to clear pirate dens who raided the Chinese coast on the Northern Filipino Coastlines, wiping out pirate dens. In 1449 it was advised to the Secretariat to keep an outpost in the region so that the travel cost of the fleet could be mitigated by a nearer outpost. It was thought about but rejected eventually due to the nearer problems with the new clashes with the Jurchen, Khalka and Tsangpo Tibetans to think about. If that had been given the go ahead, then an outpost could have been built that would eventually over time grow into a something like a colony.
As for others I don't really see it. If you ant to expand the Ming during their glory days, then making the Ming Reconquest of Vietnam lasting is a more viable option in my opinion.