Many of you will have seen this video before but I would suggest watching it again and listen carefully to his words. He says that missions will be offered to you based on your reputation with certain factions. This seems to suggest that missions are something that will seek you out rather than you chasing them and are based on your progress. There is another video where he is giving a lecture about the kickstarter at a games convention where he says this is already in the game and has 'random encounters' listed as one of the core mechanics on the board behind him. I can't find the video on youtube at the moment but as soon as I do I will put it up.
[video=youtube;s5lFiOzUDmc]https://www.youtube.com/watch?v=s5lFiOzUDmc[/video]
[video=youtube;s5lFiOzUDmc]https://www.youtube.com/watch?v=s5lFiOzUDmc[/video]