Thank you @jessegrosjean for sharing this preview app! I’m excited about the new direction. I think an HTML-based document makes a lot of sense. (I’m especially excited about having a cross-platform outliner app.)
The first thing that stood out to me about Bike was the outline-manipulation animation. They’re very smooth and slick! But I think they’re a bit too slow for me. This is probably an area where personal preference varies, but I wanted to make a plug for: 2x fast animations, and/or a setting to remove all animation in favor of instantaneous changes. (Instantaneous changes are part of what makes a native app feel native to me.)
And a very small animation issue I noticed: empty lines without disclosure triangles can sometimes have gray-background hover states. Probably unintended?