Hi EasyEd
I understand ETTR a bit differently.
Firstly ETTR has nothing to do with increasing dynamic range (dynamic range describes the ratio between the maximum and minimum measurable light intensities).
If your camera, say a D800, has 14 stops of dynamic range and you haven't clipped your histogram, then you've captured the entire dynamic range your sensor is capable of capturing from the scene.
By using ETTR you're not capturing greater dynamic range, you're just lifting your shadows (that is if you haven't clipped your histogram). If your camera can capture 12 stops of dynamic range, then that's what you'll get. (This is not strictly true, but will serve to illustrate this point)
ETTR will also not help you in capturing more dynamic range from the scene, unless by raising your exposure, you are recovering shadows that were getting clipped.
If you want to expand the dynamic range to something more than what your sensor can capture, use multiple exposures with HDR techniques to do so.
What ETTR has to do with is retaining more color information in your image. The lighter parts of your image retain more information on tonal value than the darker parts. This has to do with the way digital sensors are designed.
This example from LL might help clarify this -
A typical consumer DSLR recording 12 bits per sensel is able to record up to 4,098 separate tonal values.
If we assume a 10 stop dynamic range this is how this data is distributed...
The brightest stop = 2048 tonal values
The next brightest stop = 1024 tonal values
The next brightest stop = 512 tonal values
The next brightest stop = 256 tonal values
The next brightest stop = 128 tonal values
The next brightest stop = 64 tonal values
The darkest stop = 32 tonal values
Now at any given ISO, your sensor will capture more color information in the lighter parts of the image, than in the shadows.
It's a function of how all sensors are designed and has nothing to do with how one shoots an image.
ETTR is just a tool to maximize the capture of color information by your sensor in any given situation.
How you achieve the exposure is totally up to you. You can widen your aperture, lower shutter speed, increase ISO all with the intent to push your exposure to the right.
Should one increase ISO to achieve ETTR. Well no. Should you raise your ISO to negate shake in an image. Certainly.
Currently the way the metering in your camera is set up, the priority is not to capture the most color information your sensor is capable of capturing.
Given this information, it is up to the photographer to decide how to use it. Should one raise the ISO to achieve ETTR? Or reduce shutter speed? Or go for a larger aperture?
If it's a fast moving action scene, I would not use ETTR at the expense of raising my ISO or lowering my shutter speed to introduce motion blur to my image. If it's a landscape/architecture shot and I'm on a tripod and can lower my shutter speed, I would definitely use ETTR.
With the way our cameras are metered to middle greys currently, ETTR is just not a very convenient option. If that changes, I would see myself using it a lot more often.