Equation
Lieutenant General
Since Japan had renounced her military equipment export self embargo, Taiwan can always make request towards Japan. It isn't a complete impossibility since Australia is also making a request to obtain the Soryu class SSK with promising response.
Yeah if Japan wants to risk losing their trade status with China in which their economy is so dependent on.
Besides like I said before, it's all about the program. Taiwan submarine program (if there's going to be one) will be at a beginning state and will be costly to have one. Remember, they have to basically start from scratch, that's includes building a dry dock, a manufacturing and maintenance facilities, secure the area, have enough personnel (assuming they ALL pass the security background check) to even run, build, test, and put together a submarine kit. Oh yeah, and I haven't even mention how much are needed for weapons, operating systems, nav systems, communication systems, all the computer hardware and software and life support systems. And than you have to train sailors to operate the submarine. I just covered the basics on top of my head, I'm sure there are more. As you can see, I doubt it's plausible that ROC would want to take this route if they can see how much and how difficult it can be to run a submarine program.