Actually, this is one of those discounts that does not cost disney money. The food mark up at WDW is HUGE, even with the "discount" or savings someone gets from the dining plan, disney still makes money. Plus, most people on the dining plan do eat out more because of the dining plan and the "perceived" discount. If you talk to people who buy the DDP, they do more TS meals, character dining, etc. People that do not do the DDP usually will not eat a TS every day plus a CS every day.
This is a way for Disney to make more money and allowing people to purchase more credits is actually brilliant if Disney were to implement it (I think this is one of those survey rumors, which people think means it is happening for sure). If Disney can get people to purchase more credits, that is just more profit for them, because Disney still profits from the dining plan (and during
free dining it becomes a revenue generator).
And we won't even get into all the people that purchase the DDP and walk into a restaurant and order a burger or something which would have been cheaper to purchase OOP. Or the people that don't make reservations and only eat CS meals, so they end up severely overpaying or not even using all of their credits up.......