What is the plan for the Shenyang 6th gen. Considering that J-35 is still in development,
It also does not make sense for air force to use this plane when they already have j-36 in development. The size difference between this and J-36 is not that great to create hi-lo mix type situation.
It certainly does makes sense for the PLAAF to operate both of them. In fact, both the Chengdu's J-36 and Shenyang's J-XDS are actually complementary to one another.
This compilation which I made yesterday should provide a brief yet good explanation on the topic:
(The "dump truck" i.e. bomber refers to the still-WIP H-20.)
As for the size difference between the two - While the J-XDS is pretty much Flanker-sized based on photo and video footages, the J-36 is actually significantly larger and heavier than the J-XDS. Otherwise, why would the J-36 even need 3x large-thrust engines and all of its landing gears in dual-wheel configuration, whereas the J-XDS only needs 2x large-thrust engines and single-wheel configuration for its rear landing gear pair?
This is also the direct result of the respective roles at which the J-36 and J-XDS are expected to shoulder in the aerial warfare systems of the future, combined with the characteristics and capabilities which correspond to their aforementioned roles, as per the explanation compilation above.
isn't it too early for PLA navy to have another new carrier fighter?
It's definitely not too early. In fact, the J-XDS(H) should be arriving onboard the PLAN flat-decks just in time. In contrast, the J-35 is the one who's actually late to the show.
Besides, similar to how the F/A-XXs are meant to replace the F/A-18E/Fs and serve alongside F-35Cs onboard USN CVNs in the future - The J-XDS(H)s will be the ones to replace the J-15A/Ts and serve alongside J-35s onboard PLAN CVs and future CVNs in the coming years.