I recently learned about the
Czech Corridor, a proposal at the Paris Peace Conference to create a corridor some 80 km (or more, in some of the proposals) wide and 200 km long to allow the Slavic brothers of Czechoslovakia and Kingdom of Serbs, Croats and Slovenes to share a border. Apparently the side effect of removing the Austrian/Hungarian border was simply an unforeseen side effect, and was by no means intended to prevent any sort of Austro-Hungarian national union. That would be silly.
In the end, the proposal was shot down...mostly because neither Yugoslavia nor Czechoslovakia wanted the corridor (which was populated 60% by ethnic Hungarians, >20% by ethnic Germans, and only <20% by Slavs). Still, some groups - certain Czechoslovakian factions, pan-Slavists, Croat nationalists, and for some reason the French - pushed pretty hard for it. Hard enough that while it's incredibly unlikely, I'm don't think it's quite ASB.
So let's say that for some reason - paranoia about Austro-Hungarian union probably the most likely - the Czech corridor goes through (probably with all of it under Czechoslovakian sovereignty). What kinds of implications will this have? How pissed are the Hungarians going to be? Could it lead to closer Czechoslovak/Yugoslavian ties, even to the eventual point of union? Assuming it doesn't completely butterfly WWII, what will happen to it during and after the conflict? Could it lead to Yugoslavia being drawn into the Soviet sphere...or Czechoslovakia somehow staying neutral-ish?