Something that bothered me in EU3 all along and apparently hasn't been changed in EU4 is that Catholic countries like Poland and Hungary have eastern graphics ("graphical_culture = easterngfx"). As a result, in every one of their little cities on the map there is an Orthodox temple with onion domes. I don't know why exactly it was never possible to change it in EU3 but I still have some hope that you are going to change this in EU4 - why not do this? I don't know what else is affected by graphical_culture, but I suppose Poland and Hungary are similar enough to Bohemia and Austria to fit "westerngfx".