It makes no sense for Hungary to remain alive by now. After they terrorised the world with their terrible borders, now every player neighbour has a VC on them, plus both Brandenburg and Austria could use the breathing space. That overextension is going to cost them dearly, as it has forced them to lag behind in Admin tech and ideas, as well as causing them a headache in the form of rebels here and there for some time. I feel like the Ottomans shouldn't hesitate to join Russia in this crusade, but of course there remains the Austrian question. While they would benefit from the VC and other lands they may take, this would mean being in cahoots with the Russian and the dreaded Turk, who are already too strong as is. Therefore, this situation offers itself as a great opportunity for a massive war between groups of players.
An interesting turn is how Russia was allied to Hungary and let it get away with everything up until now! It's only logical that they try to make up their mistakes of the past now. Both sides must be careful because the war that's coming can change the balance of power for good. Not that there is a very stable one, but a change could precipitate reactions hither and thither. Most importantly, if the British system of alliances stands and Austria is drawn into a Eastern European conflict, France and Burgundy will be ripe for the taking by this Atlantic coalition.