I was discussing this with my wife 10 minutes before I saw this comment.

watch / time / clock looks and works so much better on a round interface. notifications / text / buttons look and work so much better on a square interface.

So, use a watch on one wrist (round, good looking, etc), and a smartwatch on the other wrist (square, functional, 'computer')

There's no way you can mold the two together into one 'have it all' form factor

There are a lot of mechanical watches that have rectangular watch faces, some of them very attractive and expensive.