> I don't think most people calling os.urandom have any idea how /dev/urandom behaves on their machine nor do I think most people have any idea how /dev/urandom behaves on other people's machines.

Here I invoke the "consenting adults" rule.  In Python development, we never say "The user doesn't know what they're doing here, so we need to do the right thing for them."  You must treat Python programmers as adults and assume they know what they're doing.

If the user is calling os.urandom(), which is documented as behaving like /dev/urandom, then it must behave like /dev/urandom.  We can optionally make it behave better than /dev/urandom, but not at the cost of unpredictable complexity, and not at the cost of degraded performance (unbounded blocking).