Mystery solved. You just have to make your US account a primary one on your PS4 in order to play it's purchased downloaded games in any account in the PS4. So primary accounts can have their purchases played from each user in that PS4 but all other account's purchases are restricted to the user that purchased them.

Thanks for your replies. Yeah, ewalthour, I watched that video on youtube and the only problem that was not there in PS3 is that the guy cannot play the game he DLed for free from his UK account with his US account, getting a message "This application can be started only by a user who has a license for it". This is a bit alarming as with PS3 you could buy from the US store where the prices are the cheapest and play with any account on the PS3. But maybe this is just for this game, cause it was not released yet on US, who knows. Anyway, I will tell you what happens on the weekend 14-15 Dec when I will have a EU PS4 and a US Battlefield 4. Maybe I'll purchase something from the US PSN store too, to check if that happens with all digital games or just with War Thunder.

Hey guys, I have some questions. I live in Greece and will buy a PS4 as soon as it gets here at 13th of December. How will US games in EU play? I know they'll work, but my question is about accounts. Do I have to play them in my US account in order to get trophies? From PS3 I knew that you only had to sign in to the US account in order to purchase something from the store and then you could play US games in any account you wanted from the same PS3 console, but now with the issue about being plus in order to play online I don't know if that will still be the case. Will I have to be a plus subscriber in both the US account and the EU one, or just the one I play with? Also will the DLCs work with any account or just the one puirchased, which will be the account with the same country of the disc?