Yeah I feel like it could turn into an enormous thing. Managers would be able to fill their holes with ease, without losing significant pieces. Imagine jaysblue falls out of the race, and someone scores Tulo for a fraction of the cost because it's just a rental? That's an impact player who could potentially be the difference between advancing in the playoffs, and being knocked out.
You would also rarely see older players get moved to contenders anymore. Who's going to trade for an aging bat who's verging on retirement, when you can rent out a stud in his prime for less?