Very few Taiwanese people would give up the freedoms they have in Taiwan for a move to China, just because they might get paid more. There probably should be a (unbiased) study done, but it does not match my experience.
Taiwan does get shitloads of Chinese people coming in to work, though.
Taiwanese salaries are substantially lower, yes, especially for Taiwanese. Furthermore, they have an unhealthy, ineffective work culture reminiscent of Japan. These issues need to be worked out and it is a long term plan of mine to tackle this head on and very publicly when I start a business there.
For expats, there's no need to participate in this work culture if you don't work at a majority Taiwanese company, and if you do work at such a company, you can simply annoy your coworkers by leaving at 5, you most likely won't be fired over it but will need to withstand peer pressure. Visibly Asian-heritage expats will experience this even more.
The best case scenario is the one we're discussing in the main thread - expat working internationally, but remote.
From personal experience, I can tell you that Taiwan is a fantastic place as well. Lots of engineers, absurdly low cost of living for the civic amenities (which blow away even the best that San Francisco or New York can offer), and gorgeous nature if you're into that. If you manage to learn Mandarin it'll greatly expand your access to the programming community there, but if not there's plenty of English speakers and just expats.