OK, while changing the entire computer system to accomodate DVC adding the dining plan may be "optimal" for bookkeeping, lets not forget that resort computers are already capable of encoding the plan onto the room cards, they do it for packages.
Now, let us suppose that, yes, only WDW travel currently has the "switch" built into their program. If they really were in a hurry to offer this to DVC it would be a fairly simple matter to add a free standing program at the resort level to allow all resorts to add this option at check-in...all they would need to do is add a code to your room key, just like they do for discounted DVC admission to PI. The resort would have to track the number of "credits" sold and pay Disney Dining the agreed price, again, a simple program.
I still say, they are using the MYW dining program as an incentive to purchase full price rooms. That is why it is not available at check-in for DVC, AP and FL residents. Another option would be to increase the price of the plan if it is added at check-in...but then, when does it become too pricey to be "worth it"? For instance, if they added $10, would $45 per day per adult /$20 per child be too much? Most likely it would be beyond a reasonable "break-even" point, making the program basically an expensive "convenience" (like MOST all-inclusive resort-type plans) rather than a money saver that would have broad member appeal.