Unfortunately, this is not how shortcodes work. Your solution will not reduce performance problems.
At initialization the only thing WordPress does is make a list of all shortcodes that are being registered. If you look at the order in which WordPress is loading stuff you will see that plugins are loaded before the theme and init hooks. This means that if you try to do things in a plugin which WP is no expecting at that time, nothing will happen.
One of those things is adding shortcodes. So, in a plugin you must postpone adding the shortcode until the init hook. That is what the example you are referring to means. It has nothing to do with performance. Just registering a shortcode causes no load on the server.
WP only starts doing stuff with a shortcode once it encounters one in a post. That’s when inefficiently written code will be taking its toll. The only way to reduce that is rewriting it (or removing it). You can use a plugin like T&P profiler to pin down which functions are eating most server time (disclosure: I wrote that plugin and yes, it still works, even if it hasn’t been updated for some time).