Hi Dire,
I'm not so much saying that making it simple will make it grow, just that it will make it sustainable and stable. Zup had a great and ambitious vision but several things didn't work out the way he hoped. It really seemed to take a lot of wind out of his sails when the kickstarter campaign failed. He really thought there was enough support to make it happen. Elite would have been launched with the support needed to make it run smoothly. After that he dropped the development team and did everything solo. I can only imagine how many hours he put in trying to pull it all together.
After that I think the biggest problem was trying to mix all of the different platforms. Before that it seemed that everyone was on a much more even playing field, once PCs were introduced there was no predictability of performance. Still, the game grew at the fastest rate when PCs were introduced partly because there were so many new people who had access but also because Zup was doing a lot of promoting. He even offered Fokker D8s for bringing in friends!
The subscription thing was always a problem. Paying one price for permanent access would only have worked with constant growth. It also made legal issues for kicking subscribers, for having in-game mods, for changing the game after purchase, etc. It also reduced the number of players overall just because so many either wouldn't or couldn't pay. I've always thought he should charge only for premium planes and paints and let them expire after a month or so. That would provide income without discouraging players. He also could have used premium items as promotions and rewards but I think having it so all the old players have all of the best equipment discourages new players.
DF has run its course. Unless a big investor comes along and hires a new team, Zup needs to make it easier for himself to manage. Unless a miracle happens the only sustainable solution is probably a simple version that doesn't use all his spare time and doesn't need expensive premium servers. Having no subscription fees could prevent many legal issues, fewer platforms would simplify the maintenance.
This is just what it looks like to me. I don't have any more access to info than any other player, I've just been around a while and read most of Zup's posts about game development on the forum.
Haven't played in months. I may play again someday. For now the thrill is gone.