Floating point precision isn't the problem - when your output is 8 or 10 bit resolution, floating point differences aren't a big deal.
The biggest blocking factor is amount of code that needs to be ported to make it work. High end SFX companies spend virtually all their man hours implementing new stuff. They don't have the time to go back and reimplement everything, and their customers aren't so cost sensitive that they demand it.
Well, I know of at least one very large SFX shop that skipped GPUs for now because the results were not consistent with results from the host CPUs.
But you're correct, man-hours to rewrite are more expensive than the CPU time in that application.
The biggest blocking factor is amount of code that needs to be ported to make it work. High end SFX companies spend virtually all their man hours implementing new stuff. They don't have the time to go back and reimplement everything, and their customers aren't so cost sensitive that they demand it.