Ah it's ten o clock here and I need to start going to bed early since I have to get up at 4am on wednesday for a train xD (I'm in GMT timezone) but I'll toss in a few ideas when I've got the inspiration for it and I'm down for fleshing out a branch and maybe helping with some of the writing if you get snowed under :D I think my branch would definitely be dark fantasy, sort of like... twisted alice in wonderland or brothers grimm style fairytale. Maybe a little spooky. But I might be getting the concept wrong so feel free to tell me if I've misunderstood something xD
hmm... perhaps it could start as if the Narrator is trying to get an idea about the character (like class/race/abilities) or roleplay (like the genre, setting, style) and different Iwaku members are presenting ideas (aka the choices). They each have their own door to go through. After they've all spoken, you're asked to choose your path. So at the start of the game it's like a nexus hub of all the branching paths (when it gets to the actual script/game that could be a big room you start in) though perhaps when you go down one path you've still got all the different members trying to direct their attention onto their path still.
Just some ideas. And some questions: what is the underlying motive for the in-game members directing the character down a specific path? Like you could have some deep thing behind it like at the end, the story/roleplay the character 'wins' comes to life, or it could just be a rollercoaster of fun and madness (my vote xD)
Just some ramblings. I could do some tests on Inkle for you to try if you like ^^