While answering a mailbag question for SI, Jon Wirtheim says
"If Nadal plays the U.S. Open, my name is Olga Barabanschikova; and, yeah, sadly I think the Nadal existential shot clock is ticking down to another year as well"
In the same mailbag, Wertheim says he believes that Novak will win the USOpen. He tells the rest of us that we have PTSD for bringing up Vinci d. S. Williams so often to him. He insists that Djokovic's situation is different for a number of reasons. He cited the Bo5, which you have mentioned several times, (and I agree with that. Which is one reason I think women should play Bo5 at Majors, but that's for another day/thread.) He also said that Novak doesn't have to play his own brother, and that we don't take into account the emotional toll there. I think that is an oddball point, since Serena has won plenty of Majors beating Venus, whether in the finals, or along the way. Sure, another pressure in a pressure-filled USO for her that year, but I don't think that salient of a point, as a comparison. And then he said that Novak is not playing his home Slam, as Serena was. All due respect to JW, whom I like and respect, I think that is a completely bogus point. If anything, home court support is a benefit, not a disadvantage. But that's not even really my point. It's a Major, and the pressure to win is great there, any year, for elite players. If Serena had been a first time Major contender at the USO, you might cite the pressure of winning for US tennis. But she'd already won the Open 6 times before 2015.
Bottom line, I think there are plenty of good arguments for why Novak could win the US Open and complete the CYGS, but I don't think those two are among them. He's discounting the most recent example we have at an attempt via arguments that I don't think are that valid. I do think that the most likely reason that Novak would not win the US Open this year would be the pressure. It's what got Serena. And Novak is just not better than Serena, in terms of being a champion.