Unfortunately it's very likely the button will be gone in favor of Face ID and it's going to use the case design of a previous model so it will get bigger. It's going to suck to operate when wearing a helmet and glasses.
The issue is margins.
That is an additional SKU to manage, and Apple is extremely ruthless in minimizing redundant components, as this was a major reason Apple had horrid margin in the 1990s.
All manufacturers are moving away from buttons for that reason - from automotive to consumer electronics.
The same money spent on a dedicated SKU for buttons can be spent on a better optimized OLED display to reduce lag.