Good thing I didn't delete the npdm.json I made last nightI've been looking at a few npdm's and what I'm seeing is games with the minimum kernel version 0x0030 have less syscalls. Games with minimum kernel version 0x0060 have the same syscalls as newer firmware games.
So maybe changing minimum kernel version 0x0060 should allow it to run on firmware as low as 2.0 with all the syscalls available on 5.0.
So after opening the .json in Notepad++ and editing the min kernel version to 0x0060, repacking everything into an .NSP file, and installing it, the game still launches on 5.1 but doesn't work on 4.1. After a minute or two, the Switch finally threw me the "Software has been closed due to an erro" message so it probably was trying its best to launch the game to no avail.