A new beta update is available. The raytracing implementation has been sped up significantly. The same limitations of the current implementation still apply, but the performance will be around 10x faster, as the most expensive part of the raytrace shader has been precomputed and cached.
The Material::SetRefraction method has also been exposed to Lua. The Camera::SetRefraction method is now called "SetRefractionMode".
The results are so good, I don't have any plans to use any kind of screen-space reflection effect.