Most Bibles now are clear about marking it as an addition that was not part of the original text. Even King James Bibles from 70 years ago state that the section was not in ancient manuscripts, but the editors didn't mark it out as clearly as is generally done now.

Whether or not it should be excluded is an editorial decision. Some add it in for historical interest; I'm not sure I've ever seen a Bible that completely deletes it. In my opinion, it should be excluded. But hey, who am I?

Interesting. Ought this passage to be excluded from future translations/editions of the Bible, then?

The answer to your question is no. Mark 16.16-18 is not a correct test for salvation. Mark 16.9-20 are not part of the original Bible but were added later. We disregard them (Oh, some people treat them with interest. Someone inserted them along the way for a reason. But we don't consider them authoritative).

None of the early Greek manuscripts have Mk. 16.9-20. None of them. The two major, early, complete Bibles we have (Vaticanus and Sinaiticus) don't have those verses either. The church fathers don't speak of that section as being part of Mark. Some church fathers at the end of the 2nd century mention it, so it must have existed by then, but they seem to know it wasn't there originally. Many many early fragments don't have those verses at the end of Mark. Eusebius (church historian of the 300s) says Mark ends at v. 8, and so does Jerome, Clement, Origen, Cyprian, and Cyril. Where the verses do exist on manuscripts, they are marked in such a way as to show it was thought to be an addition and not original. In other words, there is massive and consistent evidence that Mark 16.9-20 are not original to the gospel but were added later, and this was widely recognized.

So, we can confidently conclude: (a) These verses are not a correct test for salvation, and (b) No one automatically has those properties (healing, snake handling, other languages, casting out demons, immune to poison).

> It may also be that this passage refers to believers as a group, and the signs will follow the group rather than the individual.

The passage isn't legit, so it has no authority.

> Why is all of this not actually happening in the world today?

Because it's an addition and it has no authority.

Mark 16:16-18 says: "Whoever believes and is baptized will be saved, but whoever does not believe will be condemned. And these signs will accompany those who believe: In my name they will drive out demons; they will speak in new tongues; they will pick up snakes with their hands; and when they drink deadly poison, it will not hurt them at all; they will place their hands on sick people, and they will get well."

So, anyone is saved should have the following properties:

Will drive out demons
Above average language learning ability
Will pick up snakes
Immune to poison
Will heal sickness by placing of hands
Now, perhaps in many cases we have no information - it may be the case that, despite having the ability, the believer simply hasn't tried to drink poison, and so remains unaware of their immunity. But the text says that believers will (not just can) drive out demons and heal the sick.

It may also be that this passage refers to believers as a group, and the signs will follow the group rather than the individual. So groups of believers should have at least some people who can heal by laying on hands.

Why is all of this not actually happening in the world today? Are there no actual believers left?

Or, if you think this is happening in the world today, why is it not making the newspapers or being talked about anywhere?

[Required disclosure of my own views: I am an atheist and do not personally believe that "salvation" is an actual thing that exists.]