Greetings,
We definitely understand that having some type of FATE journal would be a cool way to track which FATEs you've completed. However, we'd like to add a variety of FATEs in the future, so if we were to implement a journal type of feature it would increase the amount of saved character data which would then create limitations on the number of FATEs we can add.
In other words, it comes down to a choice between whether we increase the number of FATEs or if we increase the FATE-related information, and we'd like to go in the direction of increasing the number of FATEs.