Spike: Provide a way to preview the results of conditions in post template blocks

[mogmarsh]

Description

Because conditional blocks could be used in post templates to surface different behavior based on the position of an item in the post template (e.g., show featured image only on the first item in the list) it would be nice to have a way to preview that behavior in the editor, without relying on editors saving the post and viewing it on the front-end.

Use Case

Using a Query Loop block and having different behavior for the first item in the list, and being able to see that in the editor.

Acceptance Criteria

• Devise a way to preview the results of conditional blocks in the editor when used in post templates without hiding the conditional block so that it's no longer editable/reachable.
• Create a follow-up issue to implement the recommended solution.