It will be interesting to see just how long COD holds onto the legacy platforms.
The last COD on PS3/360 was Black Ops III in 2015, two years after the release of PS4/XBO. We'll be two years passed that point when Black Ops 6 launches.
Franchises with mass casual appeal often remain on old platforms for a long time; FIFA released on PS3 and 360 until 2018, 5 years post-replacement, and Just Dance released on Wii until 2019, 7 years post-replacement.
The way we are going, I doubt this will be final COD on PS4/XBO.