Look at the last commit date on that source. It's from almost a year ago.
Cornerstone stopped production and abandoned the project due to pressures from Google over app insecurities that arose by having multiple apps run at the same time like that. Is this actually what happens? Who knows, probably not, but Google nixed the idea. Also, CM was once considering including this for their builds as well a while back, they also stopped the idea, probably due to the same pressures.
Regardless of that, there is no way this code would work out of the box for 4.2, there would have to be a bunch of changes in their code before it would work, and then who knows if it would even work as intended anymore.
We all wish it could happen, but at this point, Cornerstone isn't the way to go anymore. We'd might as well build a new system from the ground up.
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