How about the ability to put a player on a "weight training" schedule? Pretty much nobody stays at a definitive weight for their entire professional careers, many college players put on weight to be able to play professionally. 240 at DE might cut it in college, but it's not going to get the job done in the big leagues. I'm not talking about anything insane like 50-pound gains, but the potential to add 15-20 pounds over the course of one's career. The caveat would be that doing so might decrease a player's speed and agility a small amount, so there's a positive/negative aspect. Would anyone else be interested in something like this?

I fully support this idea as well assuming it's implemented well (as noted, shouldn't be easy to turn any 240 LB DE to 270 LB DE without some slight risks such as slight loss in speed potentially, etc.).