Hi, there are two types of render engines:
a) Those that provide a SDK to create render extensions. On these, we write the implementation for the plugins (actually Mental Ray, V-Ray and Maxwell).
b) When there is not a renderer SDK available, we provide to the companies our Forest SDK and they write the implementation. This mode is more limited, and several features as Forest Color are not supported.
Final Render belongs to second case. They have our SDK for third party renderers, and in fact they added Forest support in Moskito renderer.
I don't know if they found some problem with FinalRender, or there are other reasons. I would suggest you ask directly to Cebas.