Mike Moustakas tore his ACL and would figure to be out for months, perhaps the remainder of the season. If, in fact, he is done until September or longer, the Royals would need to plug the hole at third. While Plouffe isn't a gold-glover, he is solid in the field and provides a bit of power for the Royals. It is a pretty good fit and the Twins shouldn't have to worry about trading within their division when they are light years behind everyone else.
Both Plouffe and Moose would have one additional year before hitting free agency, so the Royals would probably have to trade one of them before 2017. It isn't a perfect fit, but there has to be some interest down I-35 for a proven player.