ANY changes, forking and non-forking, can get you sued for patent infringement, but not by Sun, because they've licensed their applicable patents through the CDDL. The license doesn't distinguish between forking and non-forking changes. All it tries to do is keep anyone developing CDDL software from getting sued for patent infringement, because if you introduce code subject to patent litigation to CDDL software you lose the right to do anything with it.
The CDDL purposely (in text and in intent as stated by Sun) keeps patent threats away from CDDL software and developers, yet you keep harping about Sun suing over patents in a fork.
You lose again.
They can sue though, else they would say, in writing, "we will never sue anyone, ever" while in fact they reserve that right. If Microsoft took Open Solaris and released it with a few changes and stole a lot of their business you boys would have a caniption, and be ready to sue. But let the Chinese, and you have no problem.