I don't understand the reasoning about ETTR. ETTR just says that we want maximum exposure without clipping non specular highlights. This essentially means that we are maximizing the number of photons detected. I can see there can be problems with the histogram representation, but would we have a "raw" histogram I would expect a correctly ETTR image to have maximum possible exposure.
If ETTR essentially means maximising the number of photons detected (without clipping non-specular highlights) then ETTR is only possible at base ISO. Any exposure at a higher-than-base ISO, which does not result in a clipping of highlights, is an underexposure which has been amplified in-camera to a degree specified by the ISO setting.
To put it another way, any ISO setting above base ISO is an instruction to the camera to treat the signal as though it is an underexposure and to apply the appropriate degree of amplification in accordance with those instructions.
As you know, it's long been recognised with Canon and Nikon cameras that such amplification has advantages with regard to SNR because the amplification takes place before
A/D conversion so that all further processing up-chain is effectively of a signal which is no longer underexposed.
Such an amplified signal will inevitably contain more noise than an ETTR exposure at base ISO, but the additional noise introduced as the signal is processed in-camera, starting with the A/D conversion, will have no more of an adverse effect on SNR than it would have had if the signal had been an ETTR at base ISO.
The consequence of this approach is that an ETTR exposure at ISO 200 has a better SNR than the same exposure at ISO 100, with most Canon and Nikon cameras.
The D7000 and Pentax K5 seem to have broken with this tradition. Unless you want a nice-looking review on the camera's LCD screen to show off the shot you've just taken of the nice-looking lady, it's probably better to underexpose 1 stop at base ISO than attempt an ETTR at ISO 200, or underexpose 2 stops at ISO 100 than attempt an ETTR at ISO 400 etc, etc.
The advantage of this different technique with the D7000 is that there's no danger of blowing highlights but also no disadvantage of getting a worse SNR than one might have got using an ETTR at the appropriately higher ISO in relation to the same shutter speed and aperture.