I don’t think a solid-gold Apple Watch needs to be upgradeable. Because it is solid-gold. Gold never becomes obsolete. There are companies that will pay you a significant portion of the original purchase price for your year-old iPhone so you can upgrade. There will certainly be companies that will buy a year-old, solid-gold Apple Watch for an even more significant portion of your original purchase price so you can upgrade.
(Of course, we’re talking about subsidies with the phone, but still...solid gold.)