I don't know that the Keymod owners are gonna take a bath on their rails, they'll just be a little harder to sell. Most folks aren't attaching things to the sides anyway to much of that is all moot. Given the choice the answer always was MLOK unless you wanted a specific rail and those rails were desirable and will still be for a few years.
Like Rob I have a few of the Troy TRX Extreme rails. With the continuous 12:00 and still available sling attachments I can't find a reason to ditch it. While they're obsolete in one sense I can't think if anything I want that I can't get.