To work in the new app, everything in the UI needs to be related to a standard capability or to a custom capability/capability presentation that you’ve created in the CLI. The process isn’t tough, but the documentation isn’t complete yet. Also, the new app doesn’t provide as much flexibility in how you arrange tiles though, so there are new design questions. Groovy is still around for now, so it’s not a complete rewrite.
I’ve been working on a few other DTHs and had some success, but then the whole system went down a few weeks ago. It’s supposedly back up now, but I’m getting errors that make me believe it’s still unusable. Even when it’s working, development is painful since the device and capability presentations are cached and only refresh twice a day. My advice is to wait a while before you try to work on it, and hope that they fix/improve the process.
Here’s the thread about the process: