Russia's own AIP efforts on the Lada class submarine flubbed, mainly because of the wrong direction, using fuel cells ala Germany, rather than Stirling engines, ala China and Sweden. The Russians would have to start from square one to restart in a new direction. Getting Stirling engines from China would be much easier. Another advantage the Chinese have would be Lithium battery technologies.
LOL, what I actually want is Russia to co-develop a sub with China, and then sell it to India. If India, doesn't want chinese 5G and chinese apps, it will at least pay its due share through buying subs with chinese developed tech.
Or buy more subs for the europeans for billions if they want to go down that route...