As it stands, the Bolt library depends on a C++ static kernel template extension, which is only available with the AMD OpenCL implementation. As described at http://hsa-libraries.github.io/Bolt/html/buildingBolt.html
Will Bolt get updated to support OpenCL 2.1's C++ kernel language? Link: https://www.khronos.org/news/press/khronos-releases-opencl-2.1-provisional-specification-for-public-review
We can't speak about future product plans.
I will get this to the library team as a feature request.