1-2. PP or Mango - I have a feeling that their Falco's are equal at this point (Mango's being more aggro and PP being more patient, just as in Mango v Armada), and I doubt Mango's Fox can beat PP's Falco unless Mango is playing 110% on-point.
3-4. Mew2King or HungryBox - If M2K has luck in the bracket and faces Mango, there is a chance he can win. However, he still has a massive mental barrier on PP and just gets trounced by him now. HungryBox is finally starting to figure out M2K a bit, so there is a chance that if they face in top8, he can win.
5-6. Leffen or Armada - Leffen has been improving drastically recently, and Armada has been falling off after not playing. That said, the Leffen v Armada match back in March, where Armada took a beating was a pretty convincing win for Leffen. However, I don't think Leffen is quite at that level of PP, Mango, M2K or HBox, in part because he rarely gets to play them. PP and Mango's Falcos can beat his Fox, and M2K has the Marth/FD pick or maybe another Fox ditto. I don't think Armada has completely fallen off though; I think he still has a shot at top5, depending on how much the bracket works in his favor, but not at the current big 4.
7. Hax$ - His Fox has a lot of tech skill, but it seems like it lacks a lot of fundamentals/common sense at the core. I think that his Fox could be the greatest Fox if Has would play smarter and not go for so many flashy things like double/quadruple shines. What I've seen a lot of people do is just sit patiently and wait for him to flub, and then punish him hard. I think he can break into the top8 if he just plays with more common sense. I could see him placing even at 6th (primarily due to Armada being rusty), but I don't think his Fox can contend with the likes of the top5. I think he could place just as high if he would use Falco though, and it would be more entertaining to watch.
8. aMSa - Kinda throwing an oddball out here, because after the aforementioned contenders, it's really a toss up. aMSa did extremely well at APEX 2014, and many still don't know the Yoshi matchup well -- especially a Yoshi of aMSa's caliber. He's also been practicing more and more since APEX, and though he didn't place very well in that recent Japanese MLG qualifier, that could just be because those players have more opportunities to play aMSa and adapt to his style (or bad luck in the bracket), whereas people in America/Europe have only played him a handful (maybe once or twice?) of times.