I have heard this as well and believe that Disney will change the plan to not include the tip in the future.
I have no idea how much of the DDP cost went to the CMs in the form of a tip. I know from personal experience that when the gratuity is included in my bill (i.e. some places add it to large parties) I never tip more. I actually feel a little put-off by this. However, when I am tipping on my own it's always more than the 15%. Usually if I use the Disney Dining Experience Card I tip what I saved so the server gets 20%.
However, I think the real issue here is that Disney is once again 'chipping away' at a good thing. They love to tweak these things and make it less and less cost effective to the consumer in order to maximize their profits. While the gratuity will no longer be incuded we're all paying the same price so the value goes down.
I also wouldn't be surprised to see the price of the plan go up.
This will be one of those things that Disney will keep changing until we reach the point where it's no longer cost effective to purchase the plan over paying for your own meals. I fully expect that it will be a DISer that will do the math and come up with the point at which adding the DDP is no longer worth it
I also think their is some planning and work that goes into making sure you maximize the plan - so people will have to take that into account as well when they decide it it's worth it or not.
Then once Disney sees people are not purchasing the plan they will readjust to make it a value again and the cycle will start all over. We see this all the time.
Just my thoughts
John