this seems logical to our minds, but to a computer, either each preset would have to reference something outside of the preset memory - which escapes the definition of preset memory - or the user cab list would have to check each preset one by one at some point. i wouldn't want that slowing down my axe during a performance.
it is a complicated idea as far as programming the system to do that. even if Axe-Edit did it, when you move a user cab slot, it would have to poll every single preset to see if it used that # and then change to the new #. it's not like there's a running active list of what user slots are used per preset. and with 8 possible IR slots per preset, that would take a lot of time.
maybe it could happen some day, but it's definitely not as easy as it seems. might be easier to just not move User Cabs around after they're in use.
I agree that presets should be self-contained, no external lookup table. So yes it would have to read all cab assignments in every preset and adjust if needed. I have no idea how long that would take; the III certainly does much fancier calculations at audio rate, lots of them, but there's a storage i/o piece too this too.
The idea of not moving cabs once they're in use didn't play out well for me on Helix. I'd load a bunch of cabs from a pack I got, then only want to keep a few, but still wanted to keep cabs from each pack together, bleh.
The III has way way more cab slots, so it might be less of an issue, but there are lots of cabs on offer out there...
It's also problematic that you can't tell which cabs are in use in the first place, far as I know; you couldn't on Helix. I wrote a web app that did that,
HIRB, a Helix IR Browser. Doing the remapping isn't that hard, but I didn't want to be responsible for re-writing patch files without official specs for how they were built, so it's just informational, doesn't change anything.
I've never looked at Axe III preset files, might be possible to do something similar if they're at least kind of human-readable. OTOH, Fractal stuff changes so often, might be crazy to get involved.