NOT crazy at all. Actually this is a very good idea. Being able to code makes you a much better PM and help you gain respect of engineers. It will also will help you become a better tech entrepreneur or exec if you ever choose to be.

Having some kind of hard technical skill very important. It help you tackle harder problems that arises in the future. For example let say AI becomes increasingly important. Since you know some code, you ability to lead in this a new technical field will be better than someone with no technical ability.

FYI i'm a coder and founder of a software company. Most of my time is spend on PM now.