As tensorflow/io uses Bazel to conform to TF's build system, and tensorflow/io has many projects dependencies (that uses CMake), in the past we have been manually converting CMake project to Bazel. This is really time-consuming and not very scalable.
It looks like Bazel has a project that might import CMake:
https://github.com/bazelbuild/rules_foreign_cc
We can explore and see if this fits out needs in importing CMake projects into tensorflow/io.