Yes and no
Hungary was a buffer state between austria and the ottomans, like belgium was supposed to be between France and germany. There is currently no "existential threat in your backyard/hinterland" casus belli to reflect that. Basically a conquest of hungary, if not for the extra core cost, should trigger either a crusade agains tthe turks or a jihad in austria. My feeling is that an "hinterland" system would be both realistic and historically accurate. Hinterland countries would be "buffer" coutnries whose aggression would provoke extra negative relations modifier to all other neighboring major powers. Mechanically, making an additional -100 relations pealty (cleaning @-2/year) and a CB against for any major power against another major power warring against a country whose annexion would create a common border between non-touching countries would be a welcome addition.
With the existing tools, the "don't-core-me" NI is both reasonnable, "vraisemblable" (aka doesn't shatter the suspension of disbielief while still keeping reasonnable simulationnist characterisics), and achieving it's goal (making the balkans harder to cross). So, appart for a "holy war" CB followed by tricky to balance "lust for war" modifiers (aimed at punishing crossing the border), what do you propose ?