This is a topic for discussion about the Hydra Render Delegate for integration in other applications, and USD support for the standalone Cycles.
This is mainly aimed at developers that want to improve the implementation to turn this into something usable, not a supported feature for end users. Contributions are welcome.
Editing of device settings, render settings and materials is completely missing or limited host applications, which is the main thing to improve. Choosing the render device can be done with an environment variable like