It doesn't need to happen. Digital games just need to be priced lower, as they cost the publishers much less than retail.
However, if it were up to me, if I ran something like Live or PSN, I would give store credit back on purchases instead. Let's say something like 10%. Tie it in with your subscription service. Someone buys a $60 game, they get $6 back in store credit. That's both a reward and an incentive to buy new games. Amazon often does something similar and I think it works well for them. A $10 Amazon credit will often make me pull the trigger on a new game.
That way, you get to keep the game, things are a lot less complicated, and you'd even get a reward for games you wouldn't have sold in the first place.








