I would guess the delay would be to boost sales in the market sector.
Additional photography may just be extra for the possible super deluxe luxury box set.
Clapton record goes out on October 12nd so, by marketing reasons I guess it won't be a good idea to release it at the same time. It doesn't matter is a Christmas album, it's Clapton anyway.
Now my bet is late October or early November, so no announcement until September.