Yes! 
That's exactly what I meant!
I checked on several keyboard layouts (Polish, German, Spanish) and it worked fine everywhere!
In Shortcuts window I have no junk, no diacritics or unicode characters, but only keyboard accessible ASCII characters and such "clean" shortcuts writes nicely to sigil.ini
After enabling AltGr it gets even better – it works exactly as I imagined it and as described a few posts earlier.
I can have AltGr+Q=@ on the German keyboard layout and at the same time a working shortcut Ctrl+Alt+Q that calls some function in Sigil.
I include debug log with tests for combinations with 1-5 and different modifiers (AltGr on and off).
I hope it will also work well for @RbnJrg.