Only few of the pins are known. That said you could use the known ones as gpio indeed.

Accelerometer sounds more fun.

Fortunately FAT12/16/32 are simple enough to implement. Less fortunately, USB drivers are a PITA.

It indeed would be useful. I know Linux can use this but there's no Ndless program for Nspire OS storage.

Well, they are reportedly not as fast for 2D stuff but they are much faster at 3D than the open source radeon driver. Thing is, if you want all the Linux stuff use radeon, if you want performance use Catalyst.
BTW do you use UEFI boot ? I think you can convert if you don't already because it's way better than BIOS.

LOL DJ. Happy bday Turiq !

Awww that sucks.