Cold Steep

Just watched your video ...... funny, I was just reading about that a few days ago, becuz I'm planning a brew next week. I don't know if you get BYO down there, but the March-April 2017 BYO (Brew Your Own magazine) has a good article about cold-steeping the specialty grains. It says that cold steeping doesn't have much to add in the way of extract efficiency, but you get reduced astringency (tannin extraction), increased flavor, color, free-amino nitrogen and aroma. It also says that the dark-roasted grains don't contribute significant amounts of fermentable sugars to a mash, so that's another good reason for cold steeping the dark grains to extract the color, aroma, etc., Of course the specialty grains, i.e. Vienna, Caramel, Crystal, Munich, Biscuit, etc. do add fermentable sugars to the mash, so it says that you also can then add all of the cold steeped grains to the conventional mash to recover any fermentable sugars that didn't come out during the cold steep, but the largest portion of the color, aroma etc., will already have been extracted from the darker grains. Then you would add this cold steep 'wort' near the last part of the boil to sanitize it.

Now that I have used up the fair-use doctrine to summarize that article, I have a couple of questions for you.
1.) Why is cold-steep only used in reference to extract brewing?
2.) Is there some reason why it couldn't be used for an all grain brew?

It seems to me that if you steeped the darker/specialty grains overnite, and sparged them with a liter or so of hot water as you did in your video, and then added them to the mash, they wouldn't lose much in the way of color, flavor, and aroma to the base malt during the mash. This would seem to me to be a good thing, especially if you were making a dark beer, because the color/aroma/F-an/flavor wouldn't be shared with the base malt, it would be in the first runnings/sparge of the cold steep, thereby adding more color to the final wort. It would seem to me that rather than leaving the spent base malt grains with a lot of the color, flavor, aroma, these should have been imparted to the wort rather than spent grains for the chickens/chooks, and it will now be added toward the end of the boil, keeping the color,flavor, and aroma for the final wort. Unless I am told that this is somehow a bad idea, I plan to test this theory soon with a 1 or 2 gallon all-grain brew, just to see if it works out the way I think it might. Hopefully, I have worded this correctly so that it is understandable, and not confusing. My swmbo tells me that I'm not a great communicator, so I'll take her word for it!

If these are wrong assumptions, I'd appreciate it if you could tell me why I'm wrong. You're more of a brewer than I am, I just brew for the beer, and not all of the fancy stuff. After smoking and french inhaling over the years as well as some of the odorous jobs I've held, I don't have good sense of taste or smell - my wife tells me when there's a strange smell in the house or car and then I search for the culprit!
TIA

Thanks Gash!