It's really too early. Consider the Hussites in Bohemia for example. Bohemia in 1399 EU3 is extremely stable, in history things were looking bad for them just a few years later, whereas they almost always survive and stay stable for a very long time in EU3 because it has no determinism whatsoever and the hussites are only mentioned as heretic rebels who also can appear anywhere.
Well if there will be hussite revolution event, i think it could make a difference with the fact, even while starting in 1399. Plus the great western schism should be more introduced in the early game.