What are the issues with reproducing the training process? It requires too many computing resources (which might require non-free cloud services), or it requires non-free software like GPU drivers, or both?
Whether the abstract execution system is implemented in a proprietary or free way is a separate issue. For example these days it's hard to execute x86 instructions without running some sort of proprietary microcode and/or management engine. For comparison, OpenCL has many competing implementations, including the free open source MESA graphics drivers.