This kind of LED hat is something that makes hacker mind spinning. The hat had wireless connection so, can anynone hack their “Mobile APP Bluetooth connection”? I think sending random nasty words to nearby hats could be funny if those become popular. Or sell a large number of other person’s hats as advertisement space for good money. Those were just few ideas that could be illegal to try, so best not to implement them.
Another ideas are that this is something that some hardware hackers must have made tried to make themselves. And yes they have. With Arduino and with LEDs like WS2812 this kind of ideas can be implemented quite easily. Here are some related DIY ideas for hardware hackers: