Considering how warm the 980 pro can run, the heat sink is indeed a good idea.
Hopefully the drivers reach maturity soon and it will be quite the feature, maybe a 2 TV drive saturating the PS5 maximum transfer speed.
Actually, all Samsung drives are designed to run very warm. I was reading into this with my samsung M.2 SSDs, and the drives are designed to run warm and it is not recommended to put heatsinks on the drives unless there's almost no air cooling on the drives.
This is because the NAND flash is at risk of running too cold, which can hurt performance of the drive. So if you see memory controller temps in the 90s, that's normal.
This is what i read for 960 and 970 series drives, so i'm assuming its the same for the 980s.
But, for the PS5, you really should put a heatsink on since there is no airflow. Plus with no airflow, temps should be warm enough for the NAND to operate well.