Why 50GB cartridges though ? Its not like Nintendo games needs more than 25GB for the biggest one. 32GB is enough, and you can bet most will use 16GB or even 8GB.
3rd parties ? That ship has sailed a long ago.
They could get away with even smaller than that. Internet connections are so ubiquitous these days that they could put the bare minimum of data for the game to run and then let the user download higher detail assets (which could differ depending on whether it's being played on a handheld or home console).