This article certainly provides a nice example of where element queries would be useful. All the same, I’m not convinced that it’s so hard to use current CSS to handle the issue reasonably efficiently. Much of the styling for the my_product element are shared over the two scenarios. The differences can be contained in separate CSS blocks that target a parent. For example, my_product in the sidebar can always be set to 100%, which will cover responsive variations.
So yes, it involves a bit of extra code, but nothing that’s going to break your page sizes.
In a way, I rather like the restraints forced on us by the current options in CSS, as it forces us to ask if these fancy layouts are really necessary anyway. Are sidebars even worth having any more? (Just playing devil’s advocate here. 
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