I would like to be able to refresh the data source from within the Layout Editor without needing to switch to the Data Editor.
Based on this post it sounds like it may have been there in previous versions of Glide:
Was it gumming up the Layout Editor?
It was deliberately removed, so I doubt that it will be coming back.
I don’t know exactly why it was removed, but my guess would be to discourage folks from using it too often.
It was removed because new users thought they always had to press this to update the data in the live app.