This would be simpler if it was based on #6151, as you wouldn't have to store _model_id, but could just directly instantiate the comm with the correct id in the init method. On second thought, I guess you might still want to store the model id in case open() is called more than once.

I think it would make more sense to me if we changed the widget class model_id from a property to an attribute, set the default to generating a new UUID, and then always set the comm id to the model id. Then setting the model_id becomes part of the standard trait machinery.

Closing. will open a PR to your branch, used for PR #6151 .