There are already well-defined rules, you just don't like some of the rules, e.g. you can't (today) style <select> options. Keyboard navigation is free as long as you follow the rules about which elements are focusable.

You shouldn't have to care about screen readers the same as you shouldn't have to care which browser someone uses but you always have to care about people; people who can't see or hear what you create, people who can operate a keyboard (or keyboard-equivalent) but not a mouse or touchscreen, people who can use a touchscreen but not a physical keyboard, etc.