We just booked on Eclipse for the fall and this is what we were told by our TA and by Celebrity when we called them directly:
If you select AQ, you dine in Blu....period. If you select AQ you do not have the option of reserving a table in the MDR. You may be able to change it once you board but upon initial selection of AQ, MDR is not an option.
My TA spend an hour on the phone trying to get us AQ with dinner reservations in MDR to no avail. As a result we booked Concierge Class.