I'm wondering if the eye augmentation that makes sight farther stack with equipped binoculars?

I don't know for myself, but as far as I remember reading in the official bluebottle forums they should stack.

No, they do not stack. You can sell all binoculars or scopes. Less weight etc. :)

I just tested it.

Eagle Eye+Eye Upgrade+binocluar at a hill=up to 6 hexes sight
Eagle Eye+Eye Upgrade at a hill= up to 5 hexes

and if you equip a binocluar/scope you still get the optical magnification condition.

It might change with future updates but imo it is still a sight-upgrade to use a bino/scope, at least in theory because woods/hills/high-rising buildings still block your sight, limiting your sight (wood/hill/...+1 with eagle Eye)