I'm not sure what a randomized zeroing would get you from a security perspective. You shouldn't need to be concerned about other programs observing the memory, kernels are expected to give programs only zeroed pages. If you're concerned about kernel level memory dumping, randomized zeroing isn't good enough -- it may or may not have zeroed your secrets, so that's not very helpful. Background zeroing doesn't help much here either -- FreeBSD sets a target of zeroing half the free pages, so your secrets may not be zeroed for a long time.
It seems the jury is out on the benefits from a performance perspective (DragonflyBSD took out background zeroing, saying they were unable to observe a performance difference, so simpler code is better)
Why? When taking into account the cpu cache, branch mispredictions, etc, I bet it would be slower than just zeroing it, besides it wouldn't be secure at all, imagine a process that stores a secret key, and then releases the memory, if another process can trigger the first to generate and release the key memory multiple times, they would be able to read it.
It seems the jury is out on the benefits from a performance perspective (DragonflyBSD took out background zeroing, saying they were unable to observe a performance difference, so simpler code is better)