Spent hours (literally hours) simply planning a method in my head, that would allow me to get the controller config page to work.
-=-=-

I *think* I've got it figured out, now.
The basic idea will be that I'll have TWO sets of controller code in the engine. The basic "Default" controller code, and then the redefinable controller code.
The redefinable code will only kick in when the "Framework" code is in place, because otherwise there's no define-keys screen!
When you're on the define-keys screen, navigation will use the Default keys.
In my head, that all seems to work quite well.
The tricky part is to now code it all.

I'll need a couple of arrays to store what buttons do what functions, but also what functions lead back to which buttons.
I'll need to implement a couple of #define things to let the script know that I'm using the framework.
And I'll also have to enable/disable certain abilities for different systems, eg when on iOS the "Define the Keys!" option should probably not be present at all..

Having spent the weekend with the idea bubbling in my head, it all seems to fit together.
Hopefully the actual coded version will!