Are you sure they're going to let people keep existing plays? If so, wouldn't it defeat the purpose of them reducing the DPC functionality. If they're doing it due to exploit blitzes that bug things up, wouldn't it still cause problems with the guys that have those plays already created?
Edit to add:
Also, I would guess that at least 50% of the regular D Coordinators in GLB have a pile of plays that they carry from season to season. I know my brother left me with a ton of created plays (this will be my first season without ccrogers running my Defense
) That being said, those teams would have a HUGE advantage over teams stuck with the limitations. Based on my observations from the Offensive side, positioning of dots is everything. A smidge in either direction can mean the difference between 2 yards per carry on slams to 3 yards per carry on slams. In Peewee anyways, this could be the difference between going 12-4 or 4-12.