This plan stands some chance of passing versus applying as a country, but I doubt very much it will work out. DPP lashes out in response, of course.
Update: To be clear though, even if China accepted this idea, Taiwan would not be considered a country in any way, would not have any voting power and I assume would not be able to speak at the General Assembly or anywhere else, though I'll have to research just what the hell a specialized agency is.
Here is a list of these UN specialized agencies from Wikipedia.
Second update: A loyal reader makes an important distinction:
The article in your "TVBS jumped the gun" post doesn't say the Ma admin wants Taiwan to join the UN *as* as special agency. It says to *participate in* special agencies of the UN.