@b4n wrote in 67329f2b9 "The new C styles escapesequence and taskmarker are currently mapped conservatively, and may benefit from a more visible mapping". So it looks like this never got followed up.
I think users will be unaware of this feature if it isn't on by default. I doubt people will want to turn it off, but they can if they want by looking in `filetypes.c`, which is an intuitive place.