probably a rare use case but a sys-module that checks the required firmware for the current custom theme and references it with the current installed firmware of the system during boot, moving the atmosphere/contents/0100000000001000 folder to a different location on the sd card if the theme is incompatible (and moving it back if it is) would allow for a dual-boot setup with each nand on a different firmware to use a theme on at least one of the nands (which isn’t currently possible because of atmosphere using a universally shared folder on the sd card between nands). personally i would like this to enable me to swap between my cfw sysnand while using my emunand on a lower firmware with a theme installed.
an additional benefit of it with a wider use case could be as a safety feature allowing you to update your switch without having to worry about remembering to uninstall your theme.
it could also be reworked with a similar end goal but a bit more complex execution and a more manual setup to allow you to flag specific folders in atmosphere/contents/ to be swapped in and out depending on which nand is booting. i’m not sure how feasible it is for the system-module to be able to “tell” which NAND is booting but in theory this would allow you to disable certain inessential mods, sys-modules, cheats, etc. when booting cfw sys-nand for “safer” use of online with atmosphere, while still allowing installs of deeper mods on emunand with much less hassle switching between.
many people avoid using cfw sys-nand at all due to the risk but as someone who understands and is comfortable with the risk, i would like to be able to have an extensive install of homebrew on my emunand but be comfortable going online on my sys-nand with just bare bones homebrew, in my instance being the mission control sys-module, enabled. i imagine there are others that would enjoy a similar setup.
though a con with this execution would be that with larger atmosphere installs it could increase boot time drastically as well as add additional wear on the sd card over time moving so much data around so frequently, so it is not a perfect solution.