I'd like nothing more than a break from nVidia's monopoly in rendering, but as for alternatives, the main commercial suppliers are either already CUDA locked, or about to be. Pixar Renderman XPU seems set to be Optix/CUDA locked as does Autodesk Arnold, while all other currently existing high end commercial solutions such as V-Ray, Redshift and Octane are now CUDA locked.
While Octane did briefly make a noise about breaking that lock in by supporting AMD cards - this lasted for only one version (v3.x) and did not translate to the latest (v4.x), and by their own admission in forums, they likely wont do so, citing trivial reasons for breaking from AMD support (Raja and some other guy leaving, which sounds more like an excuse than anything concrete). Considering AMD's constrained budget, I'd chalk it up to a lack of under the table money from AMD to Otoy to build and maintain a HIP/OpenCL port.
I'd certainly hope for Vulkan compute to be a viable alternative to CUDA and OpenCL in rendering, apparently Radeon ProRender has a Vulkan port already. Unfortunately ProRender is not state of the art by my reckoning of Arnold and Renderman, and Path Tracing is much more complicated than the functions that Adobe translated from OpenCL for new CC products on Android and iOS systems.
As for other renderers, there seem to be only a handful that are OpenCL and therefore cross platform, including Blender Cycles, and LuxRender - both of which are already open source, so not exactly surprising.
All things considered, the HIP/Boltzmann initiative has progressed far slower than necessary for good competition, and has only recently even begun to support consumer cards aswell as workstation cards.
Perhaps Windows support can turn this around, but I'm used to disappointment at this point where AMD is concerned.
Its obviously hard to compete against the staggering R&D advantage that nVidia has gathered with their Optix platform, and their CUDA lock in only serves to compound this as time goes by. Heres hoping with Zen 2 shuffling out the door presently that AMD will refocus some budget more significantly into both the software and hardware side of GPU's.