You guys all have really awesome ideas about what might happen and how the characters play into the events that will unfold in Dune 7.
I think it would be really cool if we could see some sort of message or remnant of the God Emperor in Dune 7, after all, he was the one who gave everyone the fighting chance.
I think whatever the threat is, humanity in all it's forms is going to have to stick together to win...and maybe that is part of the God Emperor's plans...no more in-fighting between humanity. A final bonding between everyone human?
I think Duncan serves several purposes. First, he is narratively the only link we as readers have to the first book and those original characters we love. He also has the fanatic loyalty to the Atreides and I think that might become important again in Dune 7. His actions as you said are predictable, perhaps even though Leto could not see everything in the future as he had finally introduced the no-gene, he could still predict Duncan's actions and therefore would be able to ensure that something happens. And Duncan has kickass fighting abilities that I hope we see put to good use.
I also hope that we see the worms with Leto
s pearls of consciousness play some part in what's coming. Dune has more often than not been about the Spice and the importance of all living things in balance. Hopefully we will see the worms play their part.