I've said it in previous threads, and I'll reiterate here. I LIKE this idea for Mercenaries. Because all Mercenaries is is a HIGH SCORE GAME, like in the arcades of yesteryear. The game doesn't have a story, the game doesn't have a point except to beat previously set high scores. So if I buy used, and somebody has set a high score, I've now got something to beat. I've got incentive to keep playing and getting better until I can beat their score (and if its really good and you can't beat it, lie to your friends and say you set it!)
Yes, this could show companies how to beat the trade-in issue, so that could suck. But so many people were pissed about this because it screwed this game over. Well I think it helped it. I love this idea for games whose only point is to set a high score. If they had carried this over to a story based game, I could relate to the complaints. But for this, I'm behind the idea.
They could have have a separate save for hiscores, and just be able to delete the mission progress and unlocks etc