If that is all you are worried about, I would go the simpler route and just add a surge suppressor on each input pin.
Search for
"TVS - Varistors, MOVs"
at digikey.com,
filter by in-stock.
form factor you want,
find the voltage & current you are to protect against.
Fewer components needed, and better protection provided vs blowing up your optoisolators which are not designed as shock control devices, they will fail also.