In the past companies like Roland, Korg, Yamaha ..etc would implement a Diagnostic or test mode [Often mention in the supplied service-manuals], which would help the service-centers to Diagnostic issues.
This feature is unfortunately forgotten or ignored with the development of consumer-electronic end-user behavior, where end-users are buying something, use it for a few years and then dump it or re-sell it.
What should this feature achieve?
The ability to boot the device into a Test/Diagnostic-mode, where all buttons and ports can be tested. This could maybe also make the life-easier for our brilliant moderator team, when it comes to end-user trouble-shooting on the forum.
#Durability#Sustainability
Example:
Buttons [Incl velocity, where it is featured]/jog wheel test
Port test
Midi test
SD-card test
Radio
Hardware self-test
Screen-test
Battery test
Ram check
More detailed logging with different levels (info, warn, error) with timing information.
I doubt that such are very cpu eating, we are not talking “stress test”, but purely “ functionality test”, where you focus on issues one-by-one.
That could be useful. Even as a simple system log dump over USB.
My Synth’s pads become unresponsive after it’s powered on for a few hours - all other knobs and buttons work normally and it responds to MIDI notes, just the pad grid does not do anything and I need to reboot the device. I can live with that, but this may be a symptom of some deeper underlying issue.
Y 
So that way no OS or extra stuff needed for the main units!