Matthieu Herrb shared while talking about BSD support for X.Org and KMS at FOSDEM that a Radeon KMS driver might come in Oracle Solaris 11. In Solaris 11, Oracle ported the Intel Linux KMS driver to the Solaris kernel.
Oracle is still maintaining their ported Intel KMS driver for Solaris while it might be joined by a Radeon KMS driver in Solaris 12. This information appears to be based on statements by Alan Coopersmith, an X.Org developer.
Radeon support would also require porting the complicated TTM memory management infrastructure to Solaris. Radeon Solaris support would be sought after since AMD doesn't provide any official (Catalyst) graphics driver for Solaris. Meanwhile, a Nouveau driver port to Solaris won't come since NVIDIA provides its high-quality proprietary driver to Solaris desktop users.
With the Solaris 12 X.Org plans, it's also rumoured that it will ship with X.Org Server 1.13 or 1.14. The 1.14 release is due out in March. Matching updates to the other related X.Org components would also happen for Oracle Solaris 12. It appears that Oracle is gemerally following upstream X.Org releases quite closely.
In regards to Herrb's original focus, KMS/X.Org on the BSD operating systems, that support is even worse off than Solaris with most *BSDs not even having Intel KMS support let alone Radeon, Nouveau, or the other DRM drivers. Those details from the Brussels open-source event will be covered in another Phoronix article.