Kinda saw this coming, given everything else that Charlie has on his plate, and the fact that we've heard not much on Frank or Francis in quite a while. But it's still a bummer. Says Edward Davis at indieWIRE:

[...] is the project dead? Not quite, but it doesn't seem to be moving forward either. Reps for Charlie Kaufman will only allow that the project has been "postponed," and that makes complete sense given the amount of work that Kaufman has moved on to recently, including his first novel, an HBO series and the adaptation of the sci-fi young adult novel, "Chaos Walking" for Lionsgate. (Source)

Thanks to Justin and Tim!