More convenient for the right index finger.

You'd need the "crown" on the left of the watch body, in that case. Although it would be very nice of Google to add an option to flip the interface for users who want to wear the watch "upside-down".

and the higher placement makes it less convenient for a left thumb.

Good point. I see, by the way, that the parent post was talking about the dial of the watch face, but I mistakenly interpreted that as a reference to the crown/button on the side.