Online leader boards would be awesome. They are great motivators in video pinball and for all the flaws of video pinball this one benefit is huge as a reason to keep plugging away at a game. It gives an incentive to keep playing and improving even if it's just to crack the top 1000. Would this work for real pinball, who knows, for all the reasons listed in previous post. But there's cheating even in digital pinball and it doesn't really bother me, you just learn to ignore the cheaters and move on.
Anyway, on to the when question. Stern will do it approximately two years after another pinball company does it. If no other pinball company does it first, then they will never do it.