The concept existed in other games still, it just looks different.
>Rare's failed attempt at Stop N' Swap
>dragon ball Tenkaichi 3 uses disc swapping with 1 and 2 to unlock additional gameplay modes
>Sequel games reading save data from the games that came out before it on memory cards to carry over progress, or transfer bonus rewards
>GBC Ubisoft games had hidden keys in each game that could be traded to other Ubisoft games to unlock more content using the GBC infrared port
>the Gamecube GBA adapter and the various games that supported it (my favorite was using Sonic Advance to transfer my Chao to from Sonic Adventure 2 Battle, and using it as a portable chao garden, a decent successor to the VMU chao adventure.)
>gen IV pokemon games read the GBA slot on the DS, and having different gen III Pokemon games in the GBA slot while playing made exclusive swarms of Pokemon appear in the wild in certain areas
>Metal Gear Solid Portable Ops unlocks exclusive characters for having save data from other Metal Gear games on the memory stick
Cross game interactivity is still underused though, it's such a cool concept.