With a PoD of 1946 make sure that the PRC still wins the Chinese Civil War, but they successfully manage to take Taiwan but the ROC remains doggedly in Hainan. What would the effects of such a swap be in the geopolitics of the region?
 
The distance between Hainan and mainland China is much shorter than to Taiwan, so those occasional artillery duels and incursions directly hit Hainan rather than periphery islands, as is the case with OTL’s ROC. Plus it’s tucked right in close to Vietnam, so I wonder how long it’d last anyway. For a start, it would be a little harder for the US to intervene.
Ignoring these points, it royally screws up the PRCs claim to the Spratly and Paracel islands as these are essentially south of Hainan and IOTL are administered as part of Sanya on the south coast of Hainan. Not that little details like that would get in the way of the PRC.
 
The distance between Hainan and mainland China is much shorter than to Taiwan, so those occasional artillery duels and incursions directly hit Hainan rather than periphery islands, as is the case with OTL’s ROC. Plus it’s tucked right in close to Vietnam, so I wonder how long it’d last anyway. For a start, it would be a little harder for the US to intervene.
Ignoring these points, it royally screws up the PRCs claim to the Spratly and Paracel islands as these are essentially south of Hainan and IOTL are administered as part of Sanya on the south coast of Hainan. Not that little details like that would get in the way of the PRC.
Didn't Hainan also have a large communist insurgency ?
 
IIRC what allowed the PLA to take Hainan and not Taiwan was that there were pro-communist ethnic rebels in Hainan, it was not well-fortified by the KMT, the distance to the mainland was less, and the PRC had not yet intervened in Korea (which caused the US to take the defense of Taiwan seriously).

Amphibious assaults being as difficult as they are, had the ROC planned for a better defense of Hainan, it would have likely stayed under their control. I can't imagine a scenario where the PLA manages to take Taiwan but not Hainan, as Hainan is the obvious first choice.
 
Amphibious assaults being as difficult as they are, had the ROC planned for a better defense of Hainan, it would have likely stayed under their control. I can't imagine a scenario where the PLA manages to take Taiwan but not Hainan, as Hainan is the obvious first choice.
Agreed Hainan would be target number one and it would be a much easier invasion compared to Taiwan. Maybe if Taiwan fell very early in the war it might be possible let’s say there is a home grown communist insurgency like on Hainan that weaken the islands defenses enough for Communist forces to easily invade it.
Just due to proximity alone a surviving Nationalist China in Taiwan would greatly increase tensions and the possibility of further wars later on. Imagine a Taiwan strait crisis style event happening some time in the late 50s except in the extremely narrow Qiongzhou straight. It opens up the possibility greater of shelling of the island and more navel and air skirmishes between the Nationalist and CCP forces (all of which happened during our timelines Taiwan Strait crisis).
 
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