That's why I stated that we'll have to wait for dev diaries. Still, only major change so far that devs revealed is new trade system. If Besuchov told interviewer that 'EUIII was great, but with EUIV we'll introduce many new mechanics that will take series to the another level' prospect of EUIV would look a lot more impressive. It might be PR thing to keep 'surprises' for later 'big reveal' - fingers crossed.