I think that's where we'll end up. Using different books for everyone.
And what about atheists?
"And what about atheists?"
Good budy of mine is an ex-marine, conservative, patriotic, professor of history and an atheist. His suggestion (for him) would be to swear on the Constitution. A document he knows loves and worships (as much as he worships anything).
Oh and he would gut me like a hog if he knew I called him and EX-marine. What the heck do you call Marines who are no longer in the service?
There are some religious sects (J witnesses come to mind) that don't allow swearing oaths of any kind. Some Orthodox Jews will also not swear in a court of law. It has nothing to do with what scriptures are being used, swearing in a secular court is considered by some as taking G-D's name in vain.
Courts have admitted witnesses by "affirmation" saying "Do you affirm to tell the truth?" leaving out "so help you G-D." I believe that in the 18th century this form of testimony was called a "Quaker oath."
No, we will end up swearing on nothing.