Given the slow pace of development, it's entirely reasonable that people drop out and check back in a year or two, and it seems to be happening every so often (there's typically at least one active thread of the "I'm back after a number of years: what's changed?" type at any one time (possibly enough of those that somebody who actually know the history might want to create a "This is what's happened in DF since way back (Check here first for returning players)" pinned post).
The Big Wait is going to be a bit of a challenge interest wise. I would advice Toady to keep a copy of the last release before the Big Wait on a USB or similar (e.g. an extra one in addition to the current backup system) so that crash bugs can be fixed in the "old" version (if that had been done, the weapon trap/missile break crash bug could [and should] have been fixed with an emergency release after the 0.43.X arc).
The "DF is extremely hard and has an insane learning curve" meme is probably hurting DF, and it would probably be better for DF if those spreading it would stop doing so. In my view DF has a large number of systems, which means there's a lot to learn (with much of it optional), but it isn't particularly hard as such. The UI is inconsistent and somewhat confusing, but, again, not that hard.
Myth gen may attract new players, but I doubt anything in the current arc will attract new players in themselves: it's not making big enough waves. However, new/improved features may attract cyclic players back, retain the interest of current players for longer, and may help to hook new players who check DF out anyway (if failing to hook them, it may still help planting a seed for returning later).