differences between west germany / east germany v taiwan / china
1 - population
east germany 1989 - Around 16 million
west germany 1989 - Around 62 million
east germany was about 1/4th the size of west germany in terms of population
taiwan current - Around 23 million
china current - Around 1.4 billion
china has about 61x the population of taiwan in terms of population
2 - gdp
east germany 1989 - around $300 billion
west germany 1989 - around $1.5 trillion
east germany was about 1/5th the size of west germany in terms of GDP
taiwan current - around $760 billion
china current - around $17 trillion
china has about 13x the size of taiwan's GDP
3 - time period separated
germany - around 41 years
china - around 74 years
china and taiwan have been separated nearly double the time as germany - with no reunification in sight
So in the case of East Germany vs West Germany, the West was significantly larger both in terms of GDP and population. West Germany was about 4x~5x bigger and was able to incorporate the East because they were bigger. In addition, they were separated for a shorter amount of time.. the longer it goes on the more complicated it gets.
If we look at Taiwan and China, Chinese economy and population is somewhere between 1 and 2 factors of magnitude larger. Taiwan simply does not have the capacity to incorporate China. The state apparatus in mainland China is absolutely massive - it's hard to fathom how many bureaucrats are needed to effectively run that country.
Having said all that, looking at the future of China, I sincerely doubt there will be a democratic revolution. The approval rating for the CCP is very high (much higher than democratic countries in the West). China has historically been authoritarian. They have taken the capitalist model and effectively used it in an authoritarian state. It works well for them and I don't see that changing anytime soon.
Of course, nobody can tell the future. With the accelerating pace of technology and the inevitable climate change and who knows how much radical change there will be in the coming decades.