Note: I "posted" this an hour ago and then came back and went where the hell did that post go? Forgot to fill in the Subject field. Since then there have been some similar replies but I'm just reposting it as is.
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I certainly find AyaK's Occam's Razor argument compelling. I wish I had seen the Swedish version and watched it play out.

A one player swap could be pretty interesting at this point in that tribes are still looking to win challenges, so they would be tempted to swap out their weakest competitor. With alliances already formed, however, that least athletic person may be at the core of an alliance. Also, the person is ousted in a sense but not booted, and can either turn on their former tribe for switching them or act as a mole.

Dalton, I think your animal stampede is interesting in concept but not practical. It's a game preserve, and Burnett had to sign assurances up the wazoo with the Kenyans to leave the animals undisturbed as much as possible.

As to the other tribe picking who they want, that would be one way to go, but wouldn't account for the wording of the Ep 5 preview:
so tune in to see, who's the one they dismiss
Dismiss indicates there's a decision to let someone go, not to choose someone to come over...

If this preview's accurate we have the answer in the wording that it's a one-person swap.

SB, you asked--
...if the swap happens in Day 13, then why are Days 16, 17 and 18 -- and not Days 13-15 -- the days that Susan is talking about?

Very good question. Susan is writing about Episode 6 and the twist is Episode 5, so my take is she's considering the effect of what came down, and that it or a second twist will change the traditional thinking about the Ep 6 boot.

I still see only one way to read her words: they will have team challenges on into Ep7 or beyond. That certainly is one way to stop a majority alliance from picking off the minority, since they cannot control every boot in the middle of the game.