I think you are underestimating both 3Delight and FireFly. Sure, neither of them will recreate the GI or ray tracing features that Mental Ray does, but that's not their direction: While they aren't nearly as fast, both have a lot in common with Pixar's PRMan, at least version 10 - about the same feature set (sometimes even more, PRMan 10 could not ray trace) and the same REYES algorithm on the backend. They won't win a prize in ray tracing speed but they can get any LW or C4D user's envy with their micropolygon displacement and accurate depth of field.