Ironic that the Apple Watch is the only product Apple makes where the majority of the customers would likely very much appreciate it being thinner, yet it's the only product Apple makes that isn't getting thinner every year.
Yeah, I know, needs room for battery. But where I'd be quite happy if the iPhone/iPad/Mac all were as thick as they were 5 years ago, I'd jump for joy if the Apple Watch were half its current thickness. It works fine as is, but thinner would be nice. It's also the only direction I can see them going in some future redesign, as I don't see them stepping away from the rounded rectangle layout, and I think the 38/42mm size points were likely carefully chosen.
More on-topic, it's funny sometimes to watch people (
decidedly not in this thread) debate the two sizes and whether each one is too small/large, without stating up-front their wrist size in millimeters (common in the watch field, and 5mm increments are more precise than half-inch increments, and can be used directly with Apple's band sizes which are given in millimeters).
My wrist is about 185mm, and I find the 42mm watch just about perfectly sized (aside from wanting it to be 6-8mm thick). Meaning, the display is nice and large, but it doesn't overflow my wrist, so when looking at it head-on, the straps curve pleasingly out and around my wrist, rather than dropping straight down to the underside (as I see on many giant analog watches out on the web). I wouldn't watch the watch to be noticeably larger, or I'd run into precisely that problem (dinner-plate-itis).
FWIW, the picture below shows my 42mm series 0 Space Gray Sport next to (and underneath) my much-beloved
36mm Marathon "Search & Rescue Diver’s Quartz Medium" (note this is
much smaller than your normal 40-45mm divers/military watch). I think they actually compare favorably in size.