Hmm, very interesting. I was rather split on how much closure we'd get in TUC, but this nudges me toward the "less than I was hoping for" arena, though it really depends on the details. For me its more a thing of getting big questions answered -- which clearly we will -- though I wonder if I'm expecting too much from what is, really, the mid-point of the series. I would imagine (hope) that, closure-wise, we get something at least on par with TTT: satisfying character arc conclusions, but with the over-arcing narrative remaining unrealized (kinda has to be, otherwise there'd be no point in a third series).
Dovetailing that with the spolier quote:
I was pretty much expecting this after reading & digesting TGO, but this basically seals the deal.
TAE and PoN both have many similarities in structure, it's just harder to tell since TAE is monstrous in size, by comparison. I totally expect Ishterebinth-level detail and depth for Golgotterath. The "TTT on steroids" feeling is strong, as TTT was basically some quick knot tying, set up for climax, then the attack on Shimeh. Replace Shimeh with Golgotterath and you got a stew going.
At this point I'd be shocked if TSTSNBN is a duology, unless they're absolute tomes.