It's purely speculative, I haven't heard it anywhere either. The idea might be out there somewhere else, though. To me, the idea of the "great filter" is like acknowledging that the technical challenges required to achieve type II are so great that a planet needs to maintain global peace (and other components of a healthy environment) for an incredibly long time while attempting colonization. It's certainly possible that something could go wrong after type II status, though. But if the majority are good, they might police the baddies? I dunno. We have no data, except the fact that no one's attacked us yet, or visited in the past (that we know of). It'd just be, ya know, really nice to have interstellar compassion. Imagine reppin' Earth culture at the galaxy-wide disco, and everyone's just chill af. Like I said to kleinbl00 elsewhere in these comments, it's at least comforting to know that Earth-like planets don't seem to be as rare as we once feared. So I'm sure there are plenty of non-life-bearing planets for the type III guys if they need them for target practice or whatever.
It's important to acknowledge that the Fermi Paradox, the Drake Equation and the Great Filter are all extraordinarily pompous descriptions for preposterously simple notions that are backed up by absolutely nothing but philosophy. Worse, they're backed up by philosophy, from theoretical physicists, about sociology and exobiology. No one would take them the slightest bit seriously if they were theosophical theories about physics from a bunch of biologists but here we are. For some reason, the only people allowed to talk about little green men are the guys who get itchy when their data and their models require a constant or two to work. A biological answer to "the great filter" would involve acknowledging that social organization for evolutionary purposes must directly benefit the propagation of the species. This works for ants - depending on how you count, the ants are every bit as good at this as we are. A sociological answer to "the great filter" would involve acknowledging that social organization for tribal purposes must broach Dunbar's Number. But then, Naked Mole Rats are about four inches long and can be in colonies numbering in the hundreds so that's not so great either. The fuckin' singularity cult would argue that the obvious answer to the Fermi Paradox is that once we beat Moore's Law we all disappear inside the box and give no fucks about the physical universe anymore anyway so who cares what's happening on Tau Ceti. But nobody is allowed to discuss these things when talking about SETI because it makes the physicists upset.