I really like the idea of configuring input at start 
Just a question though: From what i know this works for all Retroarch emulators – except for pifba (needs fba2x.cfg file to be manually edited) and mame emulator.
Assuming my controller’s file is USB_controller.cfg (created at start up) can this be linked with a fba2x.cfg file which will be auto generated in the right path?? fba2x.cfg typical needs these values:
[Joystick]
A_1=
B_1=
X_1=
Y_1=
L_1=
R_1=
START_1=
SELECT_1=
LEFT_1=
RIGHT_1=
UP_1=
DOWN_1=
All these values can be auto-imported from the USB_controller.cfg (or whatever the name is) right?
It is only a thought about this..
p.s I dont know if smth similar can be done for mame controls..