Well, there's also chance that Koutetsu gains new power. We don't know yet about how two-power Next like Jake gains their two power, whether they gain it together once they awaken their power(s) or it could be they lose the one they have temporary but then they recover it back along with new power.
Plus I still have the feeling that something will happen involving Maverick. He's too shady, and somehow have mysterious, villain-ish aura. At first I thought he's Mr Legend but as we know now, he's not. Some people on other forum have theory that Maverick is the one behind the assault of Barnaby's parent so he can take custody of Barnaby and he modified Barnaby's memories with that sleep machine. Because the figure of the man killed Barnaby's parent is different from when time to time. Plus Jake doesn't have Ouroboros tattoo on his arm, so perhaps Jake, even though he's Ouroboros, wasn't the one who killed Barnaby's parent.
With 7 or so episodes remain, they must have more twist up on their sleeves:anime: