You are really good at spotting things
@ahrasis
I'm sure that mod could be ported, looks like the MobileESP project is still going.
What type of things were you looking to disable for mobile? I'm sure we are still sending a full payload of JS that could be reduced to be more data friendly. Of course a pure mobile theme would also be more data friendly as well.
One cool thing about using JS is that you can use media querys in the JS with window.matchMedia() I used that in one of my demo themes to keep an element in the viewport. anyway https://developer.mozilla.org/en-US/docs/Web/API/Window.matchMedia it is ie10+ compatible so some small issues around that. But you could prevent loading or execution with simple querys like that.
The "core" idea and code of the mod can be used in Elk just by copying the file and require_once'ing it, the functions do not use any SMF-specific code, so they should Just Work
TM. Theory. :P
Use what Spuds suggested I think it's the best way, but of course if you want to disable something, depending on what you want to disable, javascript may not be enough.