The current Game engine that RF runs on currently only works with DX9. RF-X was a try to get off of the DX9 API and it did work, but it was poorly optimized and limited in functionality. RF needs to be written from the ground up to work with newer API's and hopefully they do it in the future.
..... RF needs to be written from the ground up to work with newer API's and hopefully they do it in the future.