I’m sure thousands of people have ideas of how Bezos should spend his. Bezos should spend (or not spend) in ways and things he values, to maximize what he gets out of what he’s earned. (P.S. libraries compete with his book selling business! Why wouldn’t he rather sell a ‘library pass’ on a kindle for a monthly subscription?)
Kindle is very well integrated with library services already. Also, they do sell a month-to-month "kindle unlimited" service. It kind of sucks though (last I used it, anyway).
The integration with libraries is super-cool though!