Actors on the show have been approached with requests for some hints about the upcoming season 4, but they have been very secretive about it so far, refusing to reveal anything. We can assume that many of the actors aren’t actually aware of the detailed structure of season 4 at this stage anyway, judging by the rumors that the season is still in the planning stages.
We also don’t know if the producers of the show plan to extend it beyond season 4. Netflix have enjoyed a lot of success with “House of Cards” so far, and it would certainly be a great idea for them to continue the show, but of course that depends on its ratings as well.
They have been very good throughout season 3, and if viewership numbers remain steady in season 4, we might even see production on the show ramping up as Netflix could be more motivated to release its following seasons even faster.