Ok,
I see where you are going….
Since I am on common ground system, having the addition of an Opto doesn’t do alot.
Having a TVS diode back to ground would be as effective, and less likely to self destruct.
I am going to have several of these exposed open switches in application.
Does something like a SP721 fit the bill?
(SP721 is an array of SCR/Diode bipolar structures for ESD and over-voltage protection to sensitive input circuits.)