I don't think there's any particularly unique mechanic attached to Hungary, but if there is, then maybe it could be something related to the
Holy Crown. In this time period, one could become the legitimate King of Hungary only if he (or she) was crowned:
- in Fehérvár, in the Royal Basilica,
- by the Archbishop of Esztergom,
- with the Holy Crown of Hungary.
(After the Turks took Fehérvár, that one condition of the coronation ceased to exist, but the other two remained a requirement all the way until the abolition of the kingdom in 1946.)
So perhaps there are some mechanics one has to interact with to secure the legitimacy of succession. Perhaps the benefit of this system is increased legitimacy, access to CBs related to the
claims of the Hungarian Crown or something related to the King of Hungary's claim to the style of "
Apostolic Majesty" and the
rights associated with it.
With this being said, Hungary probably is just a strong tag at the start with a very wide array of gameplay options, which makes it an ideal playtest subject.