That would be great. I didn't think you thought so, too.
I understand the drag and drop problem.
Initially, you could let users edit the layout directly in the JSON file. So Joplin would read this "layout-desktop.json" only once at startup. This is not for "standard" users, but if they can currently install a plugin, they should also be able to edit the JSON file.
Later it might be possible to implement an UI (whatever that might look like) in the options view to define the layout graphically. From which the JSON file is written then.