On Dune 3, he has already mentioned that the script is ready, however, he also mentioned that he wants to rest from the Dune universe and make another type movie. I speculate this to be Sicario 2. I also very much like to see this hehehe. I predict Dune 3 might arrive in 5 years.
Since rest of Dune books are pretty crappy (I mean after Messiah), no wonder that he is not interested in making more movies, and I hope no one else will. Regarding Sicario, I don't know if you missed it, but there is already
Sicario 2, released back in 2018.
Btw, I saw yesterday Dune 2 for the 2nd time (decent rip is finally out) and I have to say that first part was still better for me. Good luck with your bet, but I think that chances of you winning are quite low and it will be a bad film year if that ends as a best movie we saw this year. Another thing that doesn't help it is the release date, which is way too early meaning it will be very expensive to create Oscar hype once again.