DigLloyd has written a lot about aggressive ETTR and has the proof in terms of detailed results and how it reduces noise. He likewise feels ETTR needs to be a future built in feature. He's done a lot of +2EV stuff where blinkies/histogram etc. would have advised against, going well beyond manufacturer levels. But he has the results to prove it, much lower noise. Having said all that, the D4 is the last camera that needs this feature since its ISO performance is that good. Especially in the smaller sensors (m4/3, DX, CX) ETTR would be very handy. It means slower shutter speeds though, so for me an ETTR-mode would be for non-action and most of my photography is of things in motion.
The only thing I would have liked is a better full-frame video output from the D4. The D4 CX-mode video is phenomenal though, so I preferentially use that.