The good people that left in 2013 and 2014 had to have gone somewhere, right? All of them didn't just decide to not participate in bitcoin-related conversation online. So where do you think they went - Reddit? Or maybe the really stayed and their contributions are being drowned out by the increased volume and noise?
As I basically don't really bother with other forums (this one was really the first that I've ever spent much effort on) I can't really answer that but for sure I do not see regular posts from many that used to contribute regularly previously (so they are not just being drowned out but are no longer posting much if at all).
Good luck with your forum, hopefully it serves the right purpose for you and others.
We'll see - and progress is going well - initially it is probably just going to start out as a decentralised Blog platform for crypto projects to use (and I've already had some interest in it from a couple of major projects).