So interesting. I understand what you are saying, but still have ALWAYS interpreted this as a rapture event. I never thought of it as a 50/50 event….. just assumed that those in unequally yoked relationships (friendships and marriages) would have this scenario take place at the time of the rapture.There are some that suggest this is a reference to the dividing of the righteous and the unrighteous. The wheat and the tares grow together until the harvest. (Matt 13:30). The sheep and the goats are together until they are separated at the judgement. (Matt 25:31-46).
The point of this seems to be that a person cannot claim proximity to the righteous to protect his or herself from being judged. They might have lived with believers, worked with them, been part of the same family, but that won't matter at the end.
Regardless… if this verse is about the second coming…. This is still also going to happen at the rapture too! Two sleeping or working side by side…. One is taken, the other stays…