True, but you're no worse off by already having something booked. You can decide to keep what you have or switch.
I would hold off on booking the dining plan initially and just plan on adding it later. Free dining is usually only for certain resorts that have lower than average bookings on the books at that time, so you may have to switch resorts in order to get it. As noted by others, it is theoretically possible that your early booking could be the one that kicks that specific resort over the line as to whether extra discounts are needed or if free dining is offered at that resort. I wouldn't worry about that. In the past, you have been able to pay the difference to upgrade from the free dining plan to a higher tier dining plan. I wouldn't worry about those options yet until it gets announced.
As a side note, Deluxe Dining Plan is a lot of food and a lot of time-consuming sit-down meals. If that is what you want, it's your vacation, so enjoy.