Can I bring up what I think is an under-discussed pokemon: Blaziken.
Obviously, Blaze has been banned since it gained Speed Boost (BW if I am not mistaken), because of Speed Boost's ability to snowball, which makes it quickly able to outspeed pretty much the entire tier.
However, it hasn't been tried in the current meta as it was insta-banned. But the current meta contains quite a few pokemon that outspeed Blaze even at +1. Out of the unboosted mons, jolly/timid Blaze at +1 is outside by Phero, Mega-Zam, Mega-Aerodactyle, Mega Beedril (when it is added, later this month). Similarly, it is outsped by Ash Greninja and Tapu Koko if it lacks a speed boosting nature. Added to this, a number of common choice scarf users will easily outspeed Blaze at +1, and OHKO blaze (e.g. Tapu Lele, Landorus T, Garchomp, Latios, etc.).
This means that Blaze will still need to run protect to have even a chance of outspeeding many top tier threats. This in turn means it is very hard to fit swords dance on Blaze, which means it struggles to have enough power to sweep (120 physical attack and 110 special attack are pretty meh for OU - the same physical attack as regular Sharpedo, which has the same ability and a higher base speed). It also doesn't have great coverage, assuming it runs Flare Blitz and High Jump Kick, which means it is countered by most of the top tier threats. Indeed, of the A+ and S ranked, only the steel types (Mega-Metagross [without Rock Polish], Celesteela, Magearna) and Tapu Koko would struggle to consistently deal with Blaziken. It does quite well against quite a few of the lower tier threats, but many of them can beat Blaze (going down the A-'s, Zygarde, Mega-Zam, Dugtrio, Keldeo, Manaphy, Rotom-W, Salamence, Mega Venusaur).
It seems to me that Blaziken is not any better than many of the A and S ranked pokemon that currently dominate the tier, and that it is at least worth a shot in OU, to see what happens. But the introduction of lots of new threats (and Greninja's return, + Ash's, and the change of water shuriken to a special move) means I think that Blaziken deserves a chance to see if it can exist as part of a healthy metagame in OU, rather than sitting unused in Ubers, without even a chance to show its potential.
Besides, Mega-Metagross needs something to balance it's dominance in OU!