I don't know if they plan such an expansion, but having 4 players as limit in modern games is ... not the best ?

I disagree, I think a well balanced 4p game is good. Games tend to get really long when you start adding 5+ player counts without at least parts of the game being simultaneous. Throw in a coop where you're all trying to optimize individual turns? Could really drag on.

In a group of 5 people is "impossible" to play with a 4 people limit ? This game is not for my group ?