>>718196975
>So in all likelihood, someone really could develop a perfectly functional, not entirely rudimentary game that just runs from a PS2 memory card if they wanted to.
Those already exist. Aside from the previously mentioned backup games that run fine on sufficiently large SD cards, even stock memory cards can run some games. Most PS2 homebrew software is small enough to fit on a memory card, so a lot of the homebrew games can as well. Classicube can run from the memory card, for example, as can some emulators.