Earlier this year South Korea announced plans to build a locally designed sub in the 3000 ton range. An order from Taiwan could make the subs more cost effective for both sides. And delivery would probably be faster than a U.S. designed sub would be.
Well that’s someway into the future-as far as I know,the design has not been finalised,so delivery to an export customer would take time in fact,probably more time than a US yard would take to build an established design.
Then there is the whole issue of Seoul’s ties to China-trade is huge & most importantly,China holds the levers to power in Pyongyang.