Turns out the reason the current tester12 build of Linux 3DS hangs on my 3DS (at the very least) is due to it trying (and failing) to get the version of the onboard NAND (where the Nintendo-sanctioned code resides), which hangs. If I boot the known-working copy of Linux 3DS and run parted, it instantly dies due to my NAND making it say "Error: A partition cannot reside outside of the disk!"

Either the onboard NAND is dying or Linux is just being an asshole. Either way... fuck my life.