It'd be cool if they made a single-key Touch ID accessory for people who use other keyboards. Since they probably won't, I wonder if it's feasible to take the keyboard and chop it down to a smaller size.
Another user pointed out that a Watch can fill a similar void, but keeping one _just_ for authentication seems overkill.
Maybe binding the system password into the keyboard firmware is ok. Unless you need to worry about someone dumping FW or decamping chips or whatever.