I think the issue with the Jadeja concussion was that he was allowed to keep on batting after being hit. I'm not sure what the rules are around testing for a concussion right after a blow to the helmet, but ideally he would have gone off the field immediately after being hit, rather than be allowed to bat on. Having said that, there were only 4 balls left in the game, so I can understand why the test was taken in the innings break.
I don't think this is a rule that's going to be abused to the extent where it's going to be a problem. Firstly, no one is going to be willing to cop a concussion just to get an advantage over the opposition. If they were, they wouldn't be playing cricket - plenty of other sports let you trade bodily harm for glory. Even if a player were willing to do this, the resulting injury will cause them to miss several games. Jadeja was ruled out of the rest of the series as a result of the blow. Any advantage gained in this game was then lost for the upcoming matches.
Secondly, it's going to be bloody obvious if a player is copping severe blows to their skulls deliberately just to game the sub rule. If that starts happening there will be further repercussions, both from the ICC and from the fans/media. As of now, it's not a problem, and I don't see it becoming an issue in the future.
I do think it would be good practice to name the concussion subs for each player prior to the toss tho.