Pretty sure the date for DX12 is listed in the development update, IOW, someday.
DLSS is an nVidia only, and would not be necessarily be linked to DX12 support, other than perhaps DX12 is required before they’d implement it.
If they were to choose to implement it.
I thought I saw another line that they are investigating it. Problem is, as noted, it’s a limited hardware support item, so, I wouldn’t hold your breath waiting for it.