If your approach is adopted, people would simply treat /dev/random and /dev/urandom as the same thing (which I gather is your intended goal). That is fine as long as CSPRNGs are relatively easy to make. I hear that this hinges on fancy theorems like P=BPP being true, but apparently they're not proven yet.
What if... in some parallel universe it turns out that P!=BPP, and the concept of CSPRNGs is fundamentally broken, and somebody discovers a practical method to break whatever PRNG is implemented in a system? In this admittedly unlikely universe, keeping the distinction between /dev/random and /dev/urandom (i.e. the former could block indefinitely, the latter could be insecure) seems to be the safer approach. Of course in this universe, Linux would still have to pull the PRNG from /dev/random and revert back to the old behavior, but at least it's fixable. But if userland drops the distinction between /dev/random and /dev/urandom, then the problem would be fundamentally unfixable until every app reviews and decides which guarantee they want for themselves (and releases patches).
Of course your patch does not really imply the contract between the kernel and userland has changed, which is why I mentioned intention. If it is intended to change the contract, maybe it's better to wait for P=BPP before you do it? :P