Building on various threads above, I do think that a simple fix (or at least a shake up) is to mess with the standard tribe set up/merge timing. Now that they film in a set location, they can have campsites of differing types and size to drop people into. Keep them moving so that alliances and blocs can't crystallize early.
I'd also like to see some changes involving the booted to shake it up, without having them reenter. Have all the ones that aren't F3 be the jury. Or have a random draw that any 11 of the booted could be the jury, or all post-merge plus two at random from prior, etc. It's the shake up aspect, again--because if you can't just vote Older Lady off at 1 without reason or totally screw over a pre-merge ally because you'll never see them again, it might open up some new style alliances or connections. Or bomb entirely. There's a reason I don't write tv.
Also, early on we used to get more of an edit that implied this was life and death and starvation and wild animals were around the corner. As we learned about production and what camp is like, that faded because it wasn't sustainable when you've shown the camera/sound crews wandering by. I'd like to reintroduce that "life or death" angle--by gameplay, not by strategically airdropped lions. If you finished dead last in a selected challenge, you're automatically eaten by the lions or died of dysentery, etc. Or if (even with tailoring it to avoid one note challenge beasts) that's too biased, that person loses a vote or faces against the voted-out in a contest for who really leaves, etc.
A final thought before this grows into an actual novel--I'd like the season to start with Jeff facing all of them, holding up a necklace, "this is a hidden immunity idol," as he throws it into the fire, "and you won't be seeing one again this season." Or they do exist, but there are two and can only be played once, without replacement. I actually like the HII in concept, as it really did change up gameplay, but it's getting overused and changing what advantages exist from season to season could spark some new interest.