No, I'd hate playing as Daud.
You might not, but a lot of people might. Although technically, apart from having Teleportation instead of Blink, the gameplay can be the same really with no non-lethal options for him. If we are sticking to canon that is.
I don't think it's a very difficult premise to continue. The whole idea of the gameworld is a world plagued with the same sort of social injustice and inequality that afflicted our own world. Instead of a bodyguard, imagine you're a Sea Captain or whoever who gets nearly murdered and your son or whatever is taken by someone who marries your (evil) wife.
Eh, wrong. That's the premise of Dunwall, not the rest of The Isles. And secondly, making things simple isn't a bad thing. Plots are irrelevant, everything else isn't because it makes for quality content. I can make a story about an imaginary elephant and a little boy and make it into one of the deepest psychological thrillers of all time.
I'm sure the folks at Bethesda can come up with a better story, however.
Arkane...
As for DLC, I'd love to see a few extra missions like rescuing people from prison or actually seeing a Leviathan.
Rescue missions could work but the Leviathan thing is weird. Why would you want that if it's not part of the gameplay?
Anyway, what we know for sure is that Arkane were throwing ideas around for DLC before release. They said they wanted to work more with the world they created. Corvo's story is finished so the DLC will definitely feature a new protagonist and new missions. There hasn't been any word on DLC still, probably because they want to see how well the game sells.
I'd personally want to see exactly that, new locations, new stories that actually do some plot development and characterization. Maybe we can even get to see a protagonist that is not blessed by The Outsider and just uses gadgets, while another that is entirely magic focused.
There are a lot of ideas that we can throw around but before I see or hear mentions of a sequel, I want to see Arkane realizing they need to fix some things and pay more attention to them. If not then we can expect another game that falls short and I don't want that to happen.