The only problem with a British-held Taiwan is Jardine-Matheson, one of the lesser known reasons for the annexation of Hong Kong was that Jardine was based there helping providing an economic reason for the Colonial holding.
So either 1 - Jardine decides to move, 2- Jardine does not give a nice bribe to the PM to have the annexation of Hong Kong in the treaty.
Let us go with #1 - Jardine relocates to Taiwan, okay... the colonial possession takes off financially (Jardine profits help build Taiwan as it did in IRL Hong Kong) until World War Two, there would be a brief Japanese take over, it would become a place for nationalists, but the 99 year lease will come up and things might get sticky when the province has to be returned.
Let us go with #2 - Jardine stays in Hong Kong, it becomes the rich city we know today in IRL. The colonial possession suffers financially for many years until World War Two, there would be a brief Japanese take over, it would become a place for nationalists, but the 99 year lease will come up and things might get sticky when the province has to be returned.