Hangor SSP is a variant of the S26, an export variant of the Yuan with Sterling AIP.
My guess is that the PN went with a vanilla-ish build. I know we all heard the $4-5 billion US figure (from Financial Times), but I think that price included the 8 Hangors, 4 Type 054A/P frigates, and other special mission ships from China. IMO, each Hangor likely came at $300-350 m per boat, which is a great price for a mature AIP platform with reliable ASW and AShW capabilities.
That said, I can tell you that the PN is still looking for more submarines, both shallow-water attack boats
and another full-sized AIP boat. The latter is slated to replace the Agosta 90Bs by around 2040. I can't allude to the origin or make just yet, but the PN will aim for every optimal feature. Don't expect VLS because, for the ASW and AShW roles, that isn't a must-have. Rather, think about the AIP, batteries, piping, electronics management, steel, etc. You can say it's the PN's Project AZM
We've heard credible rumours of a boomer in development. But as you said, it's difficult to design, build and validate (for safety and performance). I'm sure the PN is intent on having it, but a SSBN is likely a ways out. Probably a culmination of everything after all is said and done.