(Following up the note here.)
Should we even have structural types? What if we just had nominal types only?
In favour of this: less to learn. Having two kinds of type, especially where the difference is so subtle to explain, is a significant spend on our complexity budget.
This idea initially felt surprising, since the structural approach to types is the analogue of how Unison treats terms. But maybe the analogy with terms is misleading. When you're defining a term, it is nothing other than its contents. When you're defining a type, part of what you're doing is constructing an equivalence class of terms, and it's not clear that the id-by-content idea should carry over to that.