I booked them in early April (just after the accelerator promo was opened). On
www.delta.com NO seats are selectable; on the app (on my iphone) the D1 seats are selectable (and still what I originally chose), but the "normal" FC seats are NOT.
Wishful thinking, maybe the "normal" FCs are going D1.

DL planes only have one premium cabin, D1 or F. There's no aircraft with both D1 and F cabins.