I don't currently have any space issues, but I also don't know why I would need a deleted program for a full 7-days. I think 99% of my restore program needs would be on a program I accidentally deleted (so I would know immediately). I guess it's possible that another household member deletes a show and I might not notice for a few days? In that case, keeping it around longer isn't necessarily a bad thing.
Being able to custom define the length would make it more flexible for those who don't want to use up the space.
I would prefer to define the amount of space reserved for the deleted items. For example, if I reserved 150GB of space for deleted items, it would just save the recordings indefinitely until that limit is reached. Once the limit was reached, it would prune the oldest programs. Not sure if this would create other potential issues though.