Embree is a collection of high-performance ray tracing kernels, developed at Intel and being adopted by a range of commercial renderers such as VRay or Corona. Using embree inside appleseed might lead to significant performance gain. Moreover, there are interesting side effects: support for variety of geometry types, curve types, advanced opensubdiv caching and state-of-the-art multi-segment motion blur handling.
I will be happy to work with appleseed and make it even better.
I want to thank François Beaune and Esteban Tovagliari for invaluable assistance!