True, smartwatches will never have the lifespan of a good mechanical watch, but with the minute improvement (edit: no pun intended) the S5 Brough over the S4 I can't help thinking maybe we reached a point where AW got so good we could consider keeping them 5-7 years.
One of the reason I returned my ceramic and went back to SBSS however still stems from the longevity paradox you highlighted. I don't see the point in spending twice the price when the main feature of ceramic AW is durability and I damn well know I'll be upgrading in a few years.
You could also extend this argument to SS vs. Al, but the reason I'm willing to pay that premium for steel is purely aesthetic and personal preference. And I think most people who choose ceramic over SS or Ti think the same way on another pricing scale.