Well it is by the same people who made L4D
From the creator of sm4rt:
https://dariosamo.tumblr.com/post/174384589579/hello
https://twitter.com/dariosamo
https://www.reddit.com/r/nvidia/comments/oo3fjg/looks_dlss_isnt_that_hard_to_integrate_either/
From the creator of sm4rt:
https://dariosamo.tumblr.com/post/174384589579/hello
https://twitter.com/dariosamo
https://www.reddit.com/r/nvidia/comments/oo3fjg/looks_dlss_isnt_that_hard_to_integrate_either/
Person who posted the tweet here.
I'd say both FSR and DLSS are about on the same level of difficulty, but it depends on what information the engine has. FSR only requires the lower resolution image, while DLSS needs that, a subpixel jittered output and the screen space motion vector information.
I imagine the last one will be the toughest one depending on the game/engine, but anything that implements TAA should fullfill these requirements already.
NVIDIA also provides some excellent debugging tools to make the integration much easier due to this additional requirement.
I'm by no means an expert on the technology and I haven't even finished reading most of the details in the integration guide yet, but I'd say a day of work is certainly enough to get decent results at least.
Certainly needs more days or even weeks to sort out the potential UI/UX details and any potential glitches that might pop up due to incorrect motion vectors or ghosting glitches on sudden scene transitions.