This one is proving rather tricky to get right! Feedback on previous iterations from the Full Site Editing Go / No Go discussion that took place this week indicates that seeing the pattern carousel on the canvas can be problematic.
It’s beginning to feel like one of those situations where a little friction in the UX can actually be quite helpful in helping the user to pause for a moment, and take in what is happening.
For linear end-to-end flows like this I often find that modals work well as they help establish the focus that is necessary to complete the task. So here’s a take on the pattern selection UI built in to a modal:
This modal would be triggered on mouse-up to account for blocks being dragged from the inserter on to the canvas.
A nice thing about encapsulating this flow in a modal is that it can be entirely consistent regardless of entry point. This virtue could be valuable since there are many circumstances in which a user might find themselves inserting a block pattern; creating a template from scratch, transforming a block, editing a template part, and so on.