I just conducted a test shooting with the "Standard" picture control. If I open the NEF in Capture NX2, with the new “Always use the Latest Color Reproduction Process” preference enabled, the NEF preview has the original "Standard" color tones, and "Recorded Value ([SD] Standard)" is selected by default in the Picture Control drop down menu. If I open the Picture Control menu and choose the new "[SD] Standard" picture control, the color tones change (to the new, "better" Standard tones). But -- and this is interesting -- if I toggle back to "Recorded Value ([SD] Standard)", the tones do not change back to the original Standard tones. So, once you go to the new Standard picture control, you can't go back to the recorded Standard picture control.
Even more interesting, if I open an image shot in "DX2MODE2", and change it to "Standard", I can't go back to the recorded "DX2MODE2" tones. When I select the "Recorded Value", the resulting tones are different -- darker and more saturated than even the original Standard style. My only recourse now is to change it back to the new Standard (unless I change the Picture Control preference back to "Use the Color Reproduction Process applied in camera")
So I guess I've answered my own questions.
1. Leaving the D300 set to "DX2MODE2" will still record "DX2MODE2" images, and they will look like "DX2MODE2" in the “Always use the Latest Color Reproduction Process” environment. But if I change the picture control to Standard, I can't go back to "DX2MODE2"*. So I think this means that I should always shoot in "DX2MODE2" if I ever want to use that picture control. If I want to enjoy both worlds, I would have to make a copy of the NEF first, one for "DX2MODE2" and another for Standard.
2. In the “Always use the Latest Color Reproduction Process” environment, Capture NX2 interprets the original Standard picture control as the original Standard, but only if I don't change the picture control. Once I change it, I can't go back*.
* Technically, I can go back to the original camera picture controls if I change the Picture Control preference back to "Use the Color Reproduction Process applied in camera", but this would be tedious -- and it would remove the ability to use the new "better" Standard picture control. I don't understand why Nikon did not allow for backwards compatibility here (e.g., why not allow the "DX2MODE2" control to coexist with their newer algorithms?). There's a good discussion about this problem on Flickr
I'm still undecided if I will change my preferences, but I'm leaning toward it.
Anyone have an opinion on the Standard picture control in the “Always use the Latest Color Reproduction Process” environment?