For over a decade I've ask for one small feature to a good detector.
Say for instance on the Fisher F75 detector or another machine of comparable abilities.
Add a two tone function in the motion all metal mode.
Nothing fancy, just one tone for ferrous and another for non-ferrous.
Being a computer programmer for several years I can't imagine this would be very difficult.
Now on the F75, while in motion all metal mode the machine gives better depth and also gives an ID for detected meta