Writer Louis Tenenbaum challenges some conventional wisdom in an article called 8 Things to Consider Before You Remodel to Age in Place. Among them, he suggests:
Built-in shower seats are an increasingly common feature yet are often not utilized the way they were intended because most seats are placed too far from the showerhead and controls. As a result, most are typically used to prop up your foot while shaving your legs or as a big shelf. A movable seat is a better (and less expensive) solution.
He also definitely not a fan of walk-in tubs. Curbless showers, he suggests, are a better option.