Problems emerge for a unified /dev/*random

Nowadays most devices come with a hardware random number generating device attached, typically a camera, radio, or microphone. The low bits of analog-to-digital converters provide a copious supply of entropy that the upper bits, howsoever predictable, cannot steal away.

Such devices might be more trustworthy than the "hardware RNG" instructions provided on processor cores, which we have seen demonstrated (in a recent AMD erratum) may be reliably turned off from microcode, and, we may presume, from an appropriate not-publicly-documented instruction sequence. Whether to try to defend against such an attack depends on your threat model, of course; if so, an unreliable source of random numbers might be the least of your problems. But defense in depth has rarely been a mistake.