It could also work if the game had an OS around it in the card, and you're booting from it to play every time. It would be closer to how the cartridges worked from the player perspective.

I see no problem here.

Good point :( Maybe it could work like a CD where it'll install from the card and then you need to plug it in to launch the game lol

If it's a windows game, you could put the entire Wine prefix on the card and it would be portable. The performance would probably be pretty bad though. 2.5" SATA SSDs and a docking station would work a lot better.

It requires a steam client restart for refreshing, but I've been doing this for my steam games on Linux.

On the storage settings on steam you can add a new library on the external drive and move games to it. Both the game data and the compatdata folders are moved, so you keep the savegames and the whole protonprefix intact

I dunno, cartridges don't stop being cartridges if the save data is on the console instead of the cartridge.

Disc-based consoles certainly don't put saves on the disc.

-- Frost