Stupid plan. Why do clubs need 2 extra subs? It wouldn't help the fringe/youth players, how does sitting on a bench week in, week out improve a player? Gives the manager more options but really shouldn't he be getting it right in the first place rather than getting so many opportunities to affect the outcome of games.
There would be no real achievement for youth players at getting on the bench because there's so many places, you could even give a place to a fan who places the highest bid, he'll never get on anyways.