We speak of Han and Dutch, but let's not forget of Aboriginals.
Through much of Chinese history, Taiwan was judged a piece of mud not worth occupying it, justifying it took the threat of a rump Ming loyalist state existing here for Qing forces to invade in 1680's.
Prior to that and Dutch presence, Han Chinese population was non existent (or so I understand). Han Chineses were brought in by Dutch as labor force for agriculture such as sugarcane or rice. Another feature of Han communities in Dutch Formosa was that this situation propelled the development of trade networks by Chinese merchants on the mainland Fujian, notably in Amoy.
But, speaking of Aboriginals, not speaking of the way they enforced their rule, the main cultural happenings were through Protestant missionaries they brought in. Missionaries effectively transcripted into latin script aboriginal language as part of the evangelization effort, and I tend to think that a lasting Dutch presence would have seen a better conservation of Aboriginal culture within the framework of Protestant christianity brought in by the Dutch. I'm unsure of the settlement patterns under the Qing IOTL, but I would think Dutch presence would mean less overwhelming Han population and stronger Aboriginal population, though they would be not necessarily the most populous of the two.
As for Dutch settlers, I don't know if the comparison with Indonesia is relevant. Formosa, before Dutch period, was a void: there was no previous state and political entities were relatively primitive. It's virtually a virgin land for them to settle in, no much national identity to rise later. Also, by its position, Formosa has the potential to become the Crown jewel of the Dutch empire, ideally placed for trade with China and Japan, with resources enough to enable some kind of barter trade with China (crops and mineral resources to trade with, a strategy I believe was initiated IOTL but stopped short by Koxinga invasion).
I think that's some very good points.
We have several models of Dutch settlements.
New Netherlands, which didn't last long, but it had around 9000 settlers when it was conquered. The majority European immigrants.
Dutch Caribbean, a small Dutch class of landowners lording over vast number of slaves.
South Africa was pretty much virgin land, but it was marginal, and the colony was only established for strategic reasons. All in all the Afrikans are mostly descendant from around 1000 settlers.
East Indies, the descendants of the Dutch are the Indos. In the 17-18th the Dutch kept a permanent European population in the East Indies of around 25000, this was people who travelled from Europe and returned as they retired.
So we know the Dutch was able to transport large amount of people around the world, and they was willing to do so, if there was money to earn on it.
According to Wikipedia, Taiwan had less than 100.000 people in 1662 of which a quarter was Chinese brought in by the Dutch.
Taiwan would not fit into any of these model, it's pretty much a fifth model. Which mix the other models. The Dutch seem to have had 1800 people on the island in 1662, which was more or less 2% of the population. The question are what consequences would the Chinese rebellion have, would the Dutch stop importing Chinese to the sugar cane plantage, replacing them with other groups, I have suggested Japanese, but the Dutch could also import slaves from other places, Africa are likely to far away, but what about Malays or East Indians?
The Dutch population would likely keep rising too, but I think it's unlikely they will bring Dutch farmers in. So the Dutch will likely primarily be a urban population with the rural Dutch mostly being large land owners, their managers and these families.
The Dutch will likely keep treating the Aboriginal like they did in the start, useful allies against uprising from the peasants and slaves. This give a good reason to convert them, but also like in west Africa "marrying" native women, to create a mixed race class, which can interact between the two groups. I see little reason for the Dutch to use some Chinese dialect as a local lingua franca like they did with Malay and Portuguese in East Indies. In fact they have every reason to set up Dutch as lingua franca with Aboriginals, as it cut a potential connection with the Chinese as least in the short term. If they keep using Chinese peasants solely, they will likely keep speaking Chinese dialects. But if they begin to import other groups, we will likely see the rise of a Dutch creole.
