I don't think UUVs will replace manned fleet subs of any nature in the coming few decades. Subs, by their nature, work with very limited data (no radar, no active sonar, sporadic communications). This means human intuition is very important for submarines which is why submarine crews get a special treatment in most navies. What they do is more art than science. AI will likely not reach that level for a few more decades.
SSNs will get roles that SSKs can't fullfill like anti-shipping patrols in the Pacific Ocean therefore they won't be available for missions SSKs are currently tasked with. There are just too many to replace in a reasonable time period. So I expect China to maintain a fleet of a few dozen SSKs for decades to come which means we are likely to see a Yuan successor at some point.
Besides, China is expected to initiate the construction of the SSK-Ns very soon, which will be a significant leap over the present-day SSKs in PLAN service in terms of speed, long-duration stealth and endurance. These SSK-Ns will first complement, before succeeding, the SSKs in their intended roles and (hopefully beyond the constrains of the 1IC).
UUVs, meanwhile, will be more viable to perform in the roles of:
- ISR and counter-ISR
- Communication relays and nodes
- Minelaying and minesweeping
- Seabed warfare (e.g. tapping onto/cutting enemy undersea communication cables)
