There is a very strong rumour that the next VCDX track to be announced will be “Storage and Availability” (VCDX-SAA). This will be the final track to complete the SDDC “Quad VCDX” super architect classification (Data Center, Cloud, Network and Storage). No indication of when it will be announced, just keep an eye out for it. I would imagine it will include SRM and VSAN.
There is also the hint of a management track for VCDX (probably include the vC Ops suite) and that the Implementation Expert exams (VCIX) will be developed for Data Center, Cloud and Desktop; possibly replacing the VCAP framework. The certification space of VMware Education is in a state of flux, changes are “a-happening”.