The 48mm might be this new rugged model, 48mm being the case size not the screen size so more of a Garmin Instinct/Gshock type thing with thicker plastic casing and lightweight. I’m speculating of course.
Personally, I'm not seeing the need for a rugged model. People who want extra protection buy the regular model and add a third-party protective case. There are various case options available, catering to different levels of desired protection. I think this is the best way to satisfy everyone, and I don't see a need for a change.
I wouldn’t discard a 48mm for the « rugged » model. The Garmin Fenix 6 has a 47 and a 51mm sizes. It’s the best option for outdoor, hiking, trail running and long battery life. Curious to see what Apple could come with!
I haven’t really got an opinion as it wouldn’t fit me so it’s irrelevant. I’m sure there is a market for this size for the more rotund individual so I am all for having options for people.