Taiwan needs a Plan B for submarines. I've long been an advocate for Taiwanese submarines. They would be useful as anti-submarine assets either in the Taiwan Strait or east of Taiwan to keep open their sea lines of communication in the face of Chinese submarines; pose a threat to Chinese surface ships and invasion flotillas; and pose a threat to Chinese sea lines of communication in case of war--whether an invasion or not.
One very important role that Taiwanese Harpoon-equipped submarines at sea provide that I've never seen discussed but which I think is possibly the most important function is that those subs allow us to intervene in an invasion when time is critical even before we are prepared to openly state our intention to intervene. That is, it may take time for America to take precautionary measures against Chinese action with our forward deployed forces and to mobilize resources for intervention before we state we are going to intervene. But, knowing we will intervene, it would help to actually intervene quietly very quickly.
That's where Taiwanese subs come in. As long as even one Taiwanese sub armed with Harpoons is at sea, our submarines can fire Harpoons at Chinese invasion ships and deny that the missiles are ours. But the Taiwanese can't find anyone to build them for Taiwan so far. And if it takes too long, Taiwan will lose their aging subs and before that takes place, lose even their submarine crews, delaying having an effective submarine force for even longer even if Taiwan gets new submarines. So Taiwan needs a Plan B to help with the main benefit of Taiwanese subs until Taiwan can get new subs.
I'm no engineer, but what if the Taiwanese build single-Harpoon launcher canisterss designed to be dropped by aircraft or small combatants at sea where they submerge with only a floating antenna? The Taiwanese could then fire them from shore installations using targeting data from radar or manned or unmanned platforms in or over the strait. Sure, you could use land-based, aircraft-launched, or surface-launched Harpoons more easily than doing this. But those other platforms don't provide American the cover to covertly intervene early with our own Harpoon-armed nuclear attack submarines.
Even if possible, this doesn't replace the need for Taiwanese submarines. But it would fill a gap to leverage a very important advantage of having submarines in the Taiwanese fleet until Taiwan can get those subs from someone.