One massive problem with AIS is that it is open. This opens it up for spoofing, intentional or not. The global map is littered with garbage AIS positions, but mostly in areas that do not have strong AIS coverage to begin.

To combat this, some countries have started to enforce their countries to use VMS (vessel monitoring system). I say some, but mostly the more resource rich countries - Norway being one of them. VMS also comes with the benefit of much more data capabilities, like fishing vessels sending catch data.

Sensor fusion to detect dark vessels is also a big growing thing. We use around 5 different sensors outside the usual AIS, VMS, LRIT to build vessel tracks. Some are experimental sensors, while others are seeing more mainstream use - like navigation radar sensing.

Maybe a challenge for private entities that want to create these sorts of apps, is data - buying even just AIS data can be expensive at scale. Countries that deal with this often engage in data exchange...some data provider receives data from you, you get some in return for them.