I don't think a flat rate for tip (i.e. 10 dollars for every DDP table, or 5 dollars per every DDP guest) is in the best interest for Disney if they want to maintain high service standards or encourage higher sales within their restaurants.
A flat rate will lead to exclusively volume-based service-- forget personality, conversation, recommendations. The server will adapt by getting you out and the next five dollar "head" in.
I have worked as a server in a fine-dining establishment, and I still do on occasion (its is a small, family-owned restaurant that will call me in during busy times.) While I love my guests, ultimately I am a salesperson. I am genuine, but I am not doing this for the love of foodservice. It is unreasonable to expect Disney servers to go the extra mile if there is little to no opportunity for the guest to compensate them (sure, we can all slide them extra cash, but I'd much prefer to write it on my room charge card.)
I'm not sure of the solution to the problem...Maybe to reduce the automatic gratuity (12-15%) and clearly state the percentage to guests on reciepts, then allow for an additional gratuity to be written on (either providing a credit card, or a room charge card)
I just don't know.