I don't think Canon regrets introducing the EF-S lineup. Just like I don't think Canon regrets introducing the EF-M mount either. I actually like it that Canon makes it harder to use cross mount the equipment, for which they were not designed to do. Some of the EF-S lens' rear elements would hit the FF mirror, which is why they came up with another mount in the first place. The EF-S line was designed for amateurs and hobbiests. The lenses are smaller, cheaper and less regged than their L counterparts. There is nothing wrong with that. In fact, I prefer Canon's EF/EF-S designation to Nikon's alphabet soup code. Which lenses/bodies have focus motors? Wait, the cheapest crop bodies can't use which lenses? Which ones have a manual aperture control?
I bought into the EF-S system seven years ago, before FF became affordable. I moved to FF this year. I sold the non-kit EF-S lenses for 85% of the price that I bought them. I had the 10-22 and the 17-55 f/2.8 IS. There is no rectilinear FF lens that would work on FF with a focal length range of 10 to 22mm, and the 24-70 f/2.8s cost more than the 17-55. Even now, there are still many FF users who complain that the 24-70L II doesn't have IS, which is something that crop users have been able to take advantage of for years. In a couple years, the 6D price will drop, which will decrease the price premium required to use FF systems. Consumers ultimately win with the more choices that are available.
I don't understand why Nikon users would cripple their more expensive FF cameras with crop lenses. If the crop feature gets its down to 10.7 MP, then you're better off with a crop camera with a higher pixel density, which will improve resolution. There is nothing magical about their crop feature -- it throws out the sections of the image that are physically blocked because of the smaller image circle.