Maybe a good question to ask why China would want more diesel subs at this point. It's possible they are hiding new productions, but also very likely they just decided to concentrate on nuclear subs.
China still has around 30 SSKs that were built in the 1990s and the early-2000s (035s, 039s, Kilos and improved Kilos) in the PLAN, with most of the 035s already in reserve.
These old SSKs with no AIP and less advanced stealth features and underwater cruising abilities will become easy preys for American and Japanese ASW forces as soon as they venture beyond the region with reliable surface and aerial coverage by the PLAN and PLAAF - which doesn't really extend beyond the FIC, to be honest. Anywhere beyond the Korea Strait to the north and anywhere beyond the Nansha Islands to the south is pretty much a solid no-go for these boats too.
These old undersea boats would then be just as good as useless.
It would be preferrable for China to maintain a medium-sized fleet of advanced and highly capable SSKs for (at the very least) home-front defense within the FIC Belt and perhaps in the Sea of Japan too, which means that those older SSKs have to be replaced. There are a lot of 039C/D SSKs that need to be built in order to achieve that.
Though, on the other hand, Wuchang can't be kept doing very little work if and once the PLAN has decisively pivoted towards operating a majority nuclear-powered underwater fleet in the future.
I'm genuinely curious as to whether Wuchang Shipyard is capable of/will be capable of building nuclear-powered submarines as well... Perhaps Wuchang could be relegated to build those "mini-nuke" subs, while Huludao focuses on building larger fleet SS(G)Ns and SSBNs.
If Wuchang can join China's underwater nuclear fleet buildup effort, it is feasible for reducing Huludao's burden. In the meantime, Wuchang can also serve as a backup naval yard for nuclear-powered submarine construction, in case Huludao is rendered inoperable due to enemy attacks during wartime.