First off, let me add I'm not crazy about this idea, but I can maybe see where they are going with this. The biggest thing I don't like is starting at the 25. An incomplete pass almost guarantees the other team at least 3pts because it pretty much puts them right at the field goal range of most kickers.
With the recent changes to onside kicks, it's harder than the "historical" average to recover one these days so I understand the search for a for viable option while considering the CTE fears.
If it's going to be a possibility, I'd say keep it at the 35 yard line. But still, this is going to be very bias to the better offenses in the league. A KC will do this much more often than say the Redskins, who don't simply have the firepower and will be the ones who need to do it. Kicks made it a more level playing field.