Well since they have managed to build ten ships in around 12 months, they will obviously keep going, maybe another 3 or 4 years. Once the design is sorted out, follow on units are cheaper to make due to economies of scale, the use of jigs that can be used over and over, not having to make new sets of plans (big cost), learning from previous mistakes and learning to do things better. So logic suggests another 40 units or so (possibly a bit more)
Logic suggests than in time an ASW version will be developed using the same hull. A few CY-3 missiles possibly (assuming they can fit on such a small hull) or RBU rocket lauchers at the minimum, and of course a TAS in the stern.
When you assume a cruise speed of say 15 knots, that means in one day they could cruise say 360 nautical miles. So assume they go out for a two week cruise, thats one day out, 12 days on station, then one day back. A fleet of thirty ASW versions all trailing a TAS would make it much harder for other submarines to work close to the chinese coast. Of course only a third would be at sea at any one time, but in addition to other assets, a good ten ships actively looking for submarines at any one time would be a pretty effective tool.
Note that eliminating helicopeter hangars, large guns, long endurance, SSMs, area defence SAMs, and just focusing on ASW means that you should be able to achieve this on 1400t