In order for China to make a move, they must be able to have confidence beyond doubt that their operation would succeed. As a failed annexation would cause political and economical havoc. In order for China to have high confidence in their ability to over take Taiwan, they need capability that is simply not available to them right now (Or any organization on earth for that matter) because to fight Taiwan means to wage asymmetric warfare against a technologically advanced, prepared, reasonably well funded, and determined nation.
Some considerations that China will have to face:
* Dispersed AA missile launchers (MANPADs) that will deny complete aerial superiority over Taiwan airspace. MANPADs are cheap, work without any centralized command system, can be operated by single user without much training, and can be concealed.
* Satellite and other intelligence technology that can detect boarding ships and potentially guide missiles to eliminate them. This is bad for China as boats are still arguably the highest throughput method of getting a lot of people somewhere, quickly. Aircraft will face problem with AA.
* Cruise missile counterattacks. Taiwan doesn't have that many cruise missiles, and they each don't carry a massive yield in terms of payload. However in the event of real hostility, Taiwan can deploy them against many airfields and supporting infrastructure of the China military. This will definitely at least hinder operation of many facilities.
That's just my understanding so far. And of course, things will change, so we'll see how it goes in the future.