It's a valid question, and in fact there's quite some interest in adding write features to the web app. The current version of Radicle was designed with one user per node in mind, to get things off the ground. The process of relaxing this is currently ongoing. First, to multiple users per node, which would make use-cases like the one you are sketching viable. What we'd like to avoid is to hand the key to the server, in such case, and instead generate an Ed25519 key in the browser, and sign there, with some web-compatible transport (HTTP? WebSocket?) in between. And that's just a bit more intricate than it sounds.