My creativity is infinite by not having a way to sit down and by not having vertical slabs. There's no way in the game to do these things no matter how creative you are. A trap door is (usually) not a substitute for a vertical slab and and there's literally no way to simulate sitting down. That's Microsoft saying they don't want to, it's nothing to do with us. And that's just the top two things on their rejected page.
@Advocate I think the slabs may be a technical limitation. They'd have to deal with every combination of top & bottom slab, which might involve tons of new blockstates or an overhaul of how slabs were handled and thus not be very feasible when they have other things to work on.
Or it might be another vertical slabs thing where they say it "liMitS CreAtIViTY".