I have Western colleagues from UK and Singapore who are interested in visiting Taiwan. I told them they could have a blast and Taiwan really is a visited and interesting place for a weeks visit but I still think it could be a little challenging without some Chinese.
Hiking is incredible here but they would need to go as part of organized tours in the central mountains. ThAt kind of tourism biz could be much bigger.
Diving is a thing but then again it’s more of a thing in SEA.
Probably Chinese cooking courses could also be big.
Hot springs are great too but again a little bit difficult without some Chinese and need to rent a car.
Now Taiwan isn’t any more difficult than Japan to get around and communicate, and Japan is absolutely heaving with western tourists as well as Asians so it could just be that Taiwan isn’t so famous …
Japan isn’t that friendly to foreigners either, recently I was refused service at two restaurants in a row in Tokyo just because I was a foreigner !