RT @Cody_J_Bennett
Got custom renderers working in @preactjs by implementing react-reconciler via option hooks. Here's react-three-fiber running in Preact, demo here: https://codesandbox.io/p/github/CodyJasonBennett/preact-reconciler.

I've released this under 0.x as the very creatively named preact-reconciler: https://npmjs.com/preact-reconciler.