Until we return to the daily shelling between the two sides during the second Taiwan strait crisis, anything the Chinese do can be constituted as "I'm not touching you".
I said heavy fires, not months of fires, doing a shock and awe against Taiwan then rushing in is likely to just a easy way to get lots of landing boats sunk for not much gain at all. The military forces actually needed to take over Taiwan is not something that you can hide the build up of, they will know weeks in advance and prepare accordingly, there is no fantasy scenario where the PLA rush unguarded beaches and captures Taipei in a lighting war. The only short term capitulation possible is that the civilian government surrenders, taking over Taiwan militarily would be difficult to do in the short term that you are suggesting.
		
		
	 
Landing boats sunk by what?
It takes a boat at 30kn maybe 20 minutes to hit the shore if it starts 10nm away. For a subsonic plane with paratroopers, maybe 2 minutes.
You'll get Harpoons or more likely, some antique French anti shipping missile within 2 to 20 minutes into an unknown beach anywhere surrounding the whole island?
You can't hide the buildup? There's enough forces to surround the island and put a de facto blockade right now, and how long was it since photos of equipment moving came out? 1 to 2 days?
If you said heavy fire, not months of fire, then we are somewhat in agreement? Except you believe China cannot do heavy fire the same moment the marines land, for some unknown reason. Theyre going to be courteous and do it first before probing for breaches so rebels have weeks to prepare.
You seem to have a fantasy scenario where rebels with 1970s era equipment who get their whole command chain demolished the moment China goes in can independently mobilize to guard every possible landing spot and hold against technologically superior and locally numerical superior forces that have air superiority. 
I'd buy your argument more if the average ROC fighter were like the taliban, used to independent action, surviving poor conditions and blending in the population. But they're not. 
ROC rushing to defend beachheads in itself would already be a questionable move, government forces have absolute ISR superiority and unlimited air power, going static and waiting for landing ships to come means getting smashed by MLRS and air strikes.