Hey, I’d like to refresh this topic after 2 years, because I believe that this kind of UI could be extremely useful with the new Gutenberg editor.
We have now preview and auto mode for blocks, but it’s not the most user friendly interface for more complex blocks. Gutenberg sidebar is inconvenient with repeater fields, and the auto mode can be affected by custom theme styles, and custom fields sometimes looks a bit glitchy.
Modal could solve all those issues, and also allow users to see effects of changes in real time, just like in the preview mode. If user would be able to move the modal around, it would be just perfect solution for ACF blocks in my opinion.
Let me know what you think about this ✌️